[google_maps_flutter] Rendering custom marker uses incorrect icon on iOS

### What package does this bug report belong to?

google_maps_flutter

### What target platforms are you seeing this bug on?

iOS

### Have you already upgraded your packages?

Yes

### Dependency versions

pubspec.lock

```lock
# Generated by pub
# See https://dart.dev/tools/pub/glossary#lockfile
packages:
async:
dependency: transitive
description:
name: async
sha256: e2eb0491ba5ddb6177742d2da23904574082139b07c1e33b8503b9f46f3e1a37
url: "https://pub.dev"
source: hosted
version: "2.13.1"
boolean_selector:
dependency: transitive
description:
name: boolean_selector
sha256: "8aab1771e1243a5063b8b0ff68042d67334e3feab9e95b9490f9a6ebf73b42ea"
url: "https://pub.dev"
source: hosted
version: "2.1.2"
characters:
dependency: transitive
description:
name: characters
sha256: faf38497bda5ead2a8c7615f4f7939df04333478bf32e4173fcb06d428b5716b
url: "https://pub.dev"
source: hosted
version: "1.4.1"
clock:
dependency: transitive
description:
name: clock
sha256: fddb70d9b5277016c77a80201021d40a2247104d9f4aa7bab7157b7e3f05b84b
url: "https://pub.dev"
source: hosted
version: "1.1.2"
collection:
dependency: transitive
description:
name: collection
sha256: "2f5709ae4d3d59dd8f7cd309b4e023046b57d8a6c82130785d2b0e5868084e76"
url: "https://pub.dev"
source: hosted
version: "1.19.1"
csslib:
dependency: transitive
description:
name: csslib
sha256: "09bad715f418841f976c77db72d5398dc1253c21fb9c0c7f0b0b985860b2d58e"
url: "https://pub.dev"
source: hosted
version: "1.0.2"
fake_async:
dependency: transitive
description:
name: fake_async
sha256: "5368f224a74523e8d2e7399ea1638b37aecfca824a3cc4dfdf77bf1fa905ac44"
url: "https://pub.dev"
source: hosted
version: "1.3.3"
flutter:
dependency: "direct main"
description: flutter
source: sdk
version: "0.0.0"
flutter_lints:
dependency: "direct dev"
description:
name: flutter_lints
sha256: "3105dc8492f6183fb076ccf1f351ac3d60564bff92e20bfc4af9cc1651f4e7e1"
url: "https://pub.dev"
source: hosted
version: "6.0.0"
flutter_plugin_android_lifecycle:
dependency: transitive
description:
name: flutter_plugin_android_lifecycle
sha256: "38d1c268de9097ff59cf0e844ac38759fc78f76836d37edad06fa21e182055a0"
url: "https://pub.dev"
source: hosted
version: "2.0.34"
flutter_test:
dependency: "direct dev"
description: flutter
source: sdk
version: "0.0.0"
flutter_web_plugins:
dependency: transitive
description: flutter
source: sdk
version: "0.0.0"
google_maps:
dependency: transitive
description:
name: google_maps
sha256: "5d410c32112d7c6eb7858d359275b2aa04778eed3e36c745aeae905fb2fa6468"
url: "https://pub.dev"
source: hosted
version: "8.2.0"
google_maps_flutter:
dependency: "direct main"
description:
name: google_maps_flutter
sha256: fc714bf8072e2c121d4277cb6dca23bbfae954b6c7b5d6dd73f1bc8d09762921
url: "https://pub.dev"
source: hosted
version: "2.17.0"
google_maps_flutter_android:
dependency: transitive
description:
name: google_maps_flutter_android
sha256: f1eb5ffa34ba41f8591e53ce439f78af179a506e8386a1297d0ecd202e05c734
url: "https://pub.dev"
source: hosted
version: "2.19.8"
google_maps_flutter_ios:
dependency: transitive
description:
name: google_maps_flutter_ios
sha256: "5ed8d8d0f93dfa7f5039c409c500948e98e59068f8f6fcf9105bfd07e3709d7f"
url: "https://pub.dev"
source: hosted
version: "2.18.1"
google_maps_flutter_platform_interface:
dependency: transitive
description:
name: google_maps_flutter_platform_interface
sha256: ddbe34435dfb34e83fca295c6a8dcc53c3b51487e9eec3c737ce4ae605574347
url: "https://pub.dev"
source: hosted
version: "2.15.0"
google_maps_flutter_web:
dependency: transitive
description:
name: google_maps_flutter_web
sha256: "6cefe4ef4cc61dc0dfba4c413dec4bd105cb6b9461bfbe1465ddd09f80af377d"
url: "https://pub.dev"
source: hosted
version: "0.6.2"
html:
dependency: transitive
description:
name: html
sha256: "6d1264f2dffa1b1101c25a91dff0dc2daee4c18e87cd8538729773c073dbf602"
url: "https://pub.dev"
source: hosted
version: "0.15.6"
leak_tracker:
dependency: transitive
description:
name: leak_tracker
sha256: "33e2e26bdd85a0112ec15400c8cbffea70d0f9c3407491f672a2fad47915e2de"
url: "https://pub.dev"
source: hosted
version: "11.0.2"
leak_tracker_flutter_testing:
dependency: transitive
description:
name: leak_tracker_flutter_testing
sha256: "1dbc140bb5a23c75ea9c4811222756104fbcd1a27173f0c34ca01e16bea473c1"
url: "https://pub.dev"
source: hosted
version: "3.0.10"
leak_tracker_testing:
dependency: transitive
description:
name: leak_tracker_testing
sha256: "8d5a2d49f4a66b49744b23b018848400d23e54caf9463f4eb20df3eb8acb2eb1"
url: "https://pub.dev"
source: hosted
version: "3.0.2"
lints:
dependency: transitive
description:
name: lints
sha256: "12f842a479589fea194fe5c5a3095abc7be0c1f2ddfa9a0e76aed1dbd26a87df"
url: "https://pub.dev"
source: hosted
version: "6.1.0"
matcher:
dependency: transitive
description:
name: matcher
sha256: dc0b7dc7651697ea4ff3e69ef44b0407ea32c487a39fff6a4004fa585e901861
url: "https://pub.dev"
source: hosted
version: "0.12.19"
material_color_utilities:
dependency: transitive
description:
name: material_color_utilities
sha256: "9c337007e82b1889149c82ed242ed1cb24a66044e30979c44912381e9be4c48b"
url: "https://pub.dev"
source: hosted
version: "0.13.0"
meta:
dependency: transitive
description:
name: meta
sha256: "23f08335362185a5ea2ad3a4e597f1375e78bce8a040df5c600c8d3552ef2394"
url: "https://pub.dev"
source: hosted
version: "1.17.0"
path:
dependency: transitive
description:
name: path
sha256: "75cca69d1490965be98c73ceaea117e8a04dd21217b37b292c9ddbec0d955bc5"
url: "https://pub.dev"
source: hosted
version: "1.9.1"
plugin_platform_interface:
dependency: transitive
description:
name: plugin_platform_interface
sha256: "4820fbfdb9478b1ebae27888254d445073732dae3d6ea81f0b7e06d5dedc3f02"
url: "https://pub.dev"
source: hosted
version: "2.1.8"
sanitize_html:
dependency: transitive
description:
name: sanitize_html
sha256: "12669c4a913688a26555323fb9cec373d8f9fbe091f2d01c40c723b33caa8989"
url: "https://pub.dev"
source: hosted
version: "2.1.0"
sky_engine:
dependency: transitive
description: flutter
source: sdk
version: "0.0.0"
source_span:
dependency: transitive
description:
name: source_span
sha256: "56a02f1f4cd1a2d96303c0144c93bd6d909eea6bee6bf5a0e0b685edbd4c47ab"
url: "https://pub.dev"
source: hosted
version: "1.10.2"
stack_trace:
dependency: transitive
description:
name: stack_trace
sha256: "8b27215b45d22309b5cddda1aa2b19bdfec9df0e765f2de506401c071d38d1b1"
url: "https://pub.dev"
source: hosted
version: "1.12.1"
stream_channel:
dependency: transitive
description:
name: stream_channel
sha256: "969e04c80b8bcdf826f8f16579c7b14d780458bd97f56d107d3950fdbeef059d"
url: "https://pub.dev"
source: hosted
version: "2.1.4"
stream_transform:
dependency: transitive
description:
name: stream_transform
sha256: ad47125e588cfd37a9a7f86c7d6356dde8dfe89d071d293f80ca9e9273a33871
url: "https://pub.dev"
source: hosted
version: "2.1.1"
string_scanner:
dependency: transitive
description:
name: string_scanner
sha256: "921cd31725b72fe181906c6a94d987c78e3b98c2e205b397ea399d4054872b43"
url: "https://pub.dev"
source: hosted
version: "1.4.1"
term_glyph:
dependency: transitive
description:
name: term_glyph
sha256: "7f554798625ea768a7518313e58f83891c7f5024f88e46e7182a4558850a4b8e"
url: "https://pub.dev"
source: hosted
version: "1.2.2"
test_api:
dependency: transitive
description:
name: test_api
sha256: "8161c84903fd860b26bfdefb7963b3f0b68fee7adea0f59ef805ecca346f0c7a"
url: "https://pub.dev"
source: hosted
version: "0.7.10"
vector_math:
dependency: transitive
description:
name: vector_math
sha256: d530bd74fea330e6e364cda7a85019c434070188383e1cd8d9777ee586914c5b
url: "https://pub.dev"
source: hosted
version: "2.2.0"
vm_service:
dependency: transitive
description:
name: vm_service
sha256: "046d3928e16fa4dc46e8350415661755ab759d9fc97fc21b5ab295f71e4f0499"
url: "https://pub.dev"
source: hosted
version: "15.1.0"
web:
dependency: transitive
description:
name: web
sha256: "868d88a33d8a87b18ffc05f9f030ba328ffefba92d6c127917a2ba740f9cfe4a"
url: "https://pub.dev"
source: hosted
version: "1.1.1"
sdks:
dart: ">=3.11.3 <4.0.0"
flutter: ">=3.38.0"
```

### Steps to reproduce

Launch the app code in main.dart
Press refresh (or don't, sometimes this happens on first load).

### Expected results

There should be 3 of each colour as happens when using the default markers, or when the markers are updated as one large block instead of one-by-one

### Actual results

Sometimes the 1st or 3rd marker are red instead of using the icon they were assigned. Their on tap reports correctly, it seems to just be visual.

### Code sample

Code sample
See this gist:
https://gist.github.com/LeoBoundArch/07bd92511f6a2bf6d5886b4452842b37

### Screenshots or Videos

Screenshots / Video demonstration

https://github.com/user-attachments/assets/465f5ba6-4bfa-4d83-ae24-54fa6e8c8a10

### Logs

Logs

```console
```

### Flutter Doctor output

Doctor output

```console
[✓] Flutter (Channel stable, 3.41.5, on macOS 26.4.1 25E253 darwin-arm64, locale en-GB) [691ms]
• Flutter version 3.41.5 on channel stable at /Users/leobound/fvm/versions/stable
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision 2c9eb20739 (6 weeks ago), 2026-03-17 16:14:01 -0700
• Engine revision 052f31d115
• Dart version 3.11.3
• DevTools version 2.54.2
• Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop,
enable-android, enable-ios, cli-animations, enable-native-assets, omit-legacy-version-file,
enable-lldb-debugging, enable-uiscene-migration

[✓] Android toolchain - develop for Android devices (Android SDK version 36.0.0) [3.0s]
• Android SDK at /Users/leobound/Library/Android/sdk
• Emulator version 35.5.10.0 (build_id 13402964) (CL:N/A)
• Platform android-36, build-tools 36.0.0
• Java binary at: /opt/homebrew/opt/openjdk@17/bin/java
This JDK is specified in your Flutter configuration.
To change the current JDK, run: `flutter config --jdk-dir="path/to/jdk"`.
• Java version OpenJDK Runtime Environment Homebrew (build 17.0.17+0)
• All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 26.4.1) [1,738ms]
• Xcode at /Applications/Xcode.app/Contents/Developer
• Build 17E202
• CocoaPods version 1.16.2

[✓] Chrome - develop for the web [6ms]
• Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Connected device (3 available) [6.6s]
• iPhone 17 Pro Max (mobile) • E74AF093-F7C5-4F1A-B883-947629647396 • ios • com.apple.CoreSimulator.SimRuntime.iOS-26-2 (simulator)
• macOS (desktop) • macos • darwin-arm64 • macOS 26.4.1 25E253 darwin-arm64
• Chrome (web) • chrome • web-javascript • Google Chrome 147.0.7727.138
! Error: Browsing on the local area network for Leo Bound’s iPhone. Ensure the device is unlocked and attached with a cable or associated with the same local
area network as this Mac.
The device must be opted into Developer Mode to connect wirelessly. (code -27)

[✓] Network resources [258ms]
• All expected network resources are available.

• No issues found!
```