Push notification issues with custom matrix homeserver and sygnal

### Steps to reproduce

1. Install element
2. Trigger push notification for a user
3. First notification comes up as "MESSAGE" without any info describing the push notification
4. All consecutive notifications after that show up fine.

### Outcome

Expected behaviour is the notification banner should stay same throughout each push notification event.

### Your phone model

iPad Mini 5

### Operating system version

iOS

### Application version

14.6/15

### Homeserver

_No response_

### Will you send logs?

No

No source files or tests are named. Start by reproducing the first and subsequent push notifications on an iPad running iOS with a custom Matrix homeserver and Sygnal, then compare their payload handling; done means every notification banner consistently includes the expected information.

Written by the indexing model from the issue text.