Severe dashboard loading slowness on iOS 27 public beta — LAN connections healthy, server healthy, fresh server re-registration does not help

App version: 2026.7.2 (also reproduced on 2026.7.1, and on the TestFlight build)
iOS: iOS 27 public beta — reproduced identically on iPhone 16 Pro Max and iPad
HA Core: 2026.x (HAOS on x86 NUC), plain HTTP on port 8123 on LAN, Nabu Casa for external

Symptom
Since ~14 July (shortly after both devices moved to the iOS 27 public beta), the app is extremely slow loading and navigating dashboards when connected via the internal URL on home WiFi —
every page navigation takes 3–5+ seconds. The same HA instance is fast from a Linux laptop browser on the same WiFi, and fast via Nabu Casa Cloud from the same iOS devices.

What I've verified (with packet captures on the HA host)
- TCP handshakes from the iOS devices complete in <10ms; no retransmits, no resets — the network path is healthy.
- HA answers HTTP requests in ~1ms; HA logs over 12.5h show zero HTTP-server errors, zero ip_ban/auth issues for the device IPs.
- App status screen shows "Connected via Internal URL", WebSocket: Connected — yet performance is still poor.
- In one capture, the cold-opened app made zero LAN connections to the server and appears to have routed via the cloud instead, despite correct Internal URL + SSID config and Location
permission set to Always + Precise.
- App Event Log shows repeated "Failed to fetch device registry on server Home" (Network Request), detail: {"error": "The operation couldn't be completed. (HAKit.HADataError error 1.)"} —
recurring across the day.
- Earlier in the investigation (pre-2026.7.1-update), captures showed the app sending TLS ClientHellos to the plain-HTTP port (aiohttp 400: Received HTTPS traffic on an HTTP port); that
behaviour disappeared after updating — mentioning in case it's related history.

Ruled out
- Tailscale/VPN: fully disabled/signed out on the devices for 30+ min — no change.
- DNS: bare-IP internal URL equally slow.
- HSTS/website data: cleared — no change (fixed Safari, not the app).
- Location permission: Always + Precise ON; internal URL and SSID correctly configured.
- Server-side streaming (go2rtc ICE misconfig) found and fixed — camera loads improved, app navigation still slow.
- Deleted the server from the app and re-registered fresh — no improvement.

Expected: Dashboard navigation over LAN should be near-instant, as it was for 7+ years prior and still is from a desktop browser on the same network.

Happy to provide: further packet captures from the HA host, app event logs, or a debug build test.

I fully appreciate IOS 27 is new and just feeding back to help

Start by reproducing the dashboard delay on the iPhone or iPad using the internal URL while collecting the app Event Log and HA-host packet captures. Compare LAN and Nabu Casa behavior, focusing on the repeated device-registry fetch failures and unexpected cloud routing; done means LAN dashboard navigation is near-instant without those failures.

Written by the indexing model from the issue text.