WebUI reopens after successful sign up

### Before opening, please confirm:

- [X] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-android/issues?q=is%3Aissue+) and [discussions](https://github.com/aws-amplify/amplify-android/discussions).

### Language and Async Model

Kotlin - Coroutines

### Amplify Categories

Authentication

### Gradle script dependencies

```toml
// Put output below this line
amplify = "2.25.1"

amplifyframework-core = { module = "com.amplifyframework:core-kotlin", version.ref = "amplify" }
amplifyframework-aws-auth-cognito = { module = "com.amplifyframework:aws-auth-cognito", version.ref = "amplify" }

```

### Environment information

```
# Put output below this line
------------------------------------------------------------
Gradle 8.11.1
------------------------------------------------------------

Build time: 2024-11-20 16:56:46 UTC
Revision: 481cb05a490e0ef9f8620f7873b83bd8a72e7c39

Kotlin: 2.0.20
Groovy: 3.0.22
Ant: Apache Ant(TM) version 1.10.14 compiled on August 16 2023
Launcher JVM: 17.0.12 (JetBrains s.r.o. 17.0.12+1-b1207.37)
Daemon JVM: /Users/dawidhyzy/Library/Java/JavaVirtualMachines/jbr-17.0.12-1/Contents/Home (no JDK specified, using current Java home)
OS: Mac OS X 15.1.1 aarch64

```

### Please include any relevant guides or documentation you're referencing

_No response_

### Describe the bug

After a successful signup, the WebUI closes and then reopens.
I can see in my logs that I received a successful result.
I can also see logs from `AuthClient`

```
2024-12-20 11:45:43.990 9663-9663 AuthClient com.xxx.yyy.zzz D Handling auth redirect response
2024-12-20 11:45:44.037 9663-9663 AuthClient com.xxx.yyy.zzz D CustomTabsManagerActivity was created with a null state.
```

### Reproduction steps (if applicable)

_No response_

### Code Snippet

```java
// Put your code below this line.

```

### Log output

```
// Put your logs below this line

```

### amplifyconfiguration.json

_No response_

### GraphQL Schema

```graphql
// Put your schema below this line

```

### Additional information and screenshots

_No response_

Start by tracing the authentication redirect in AuthClient and the creation of CustomTabsManagerActivity, using the reported logs as the initial reproduction clue. Investigate why the WebUI closes and reopens after successful signup, including the null state message. Done means a successful signup closes the WebUI without reopening and the redirect completes correctly.

Written by the indexing model from the issue text.