IOS VOIP notifications getting significantly delayed if app is closed/in background

### Steps to reproduce

1. Make sure sygnal is set up properly for VOIP, log is also showing correctly configured
2. Make a VOIP call to your iOS device

### Outcome

#### What did you expect?
VOIP notifications should get triggered and the phone should ring immediately

#### What happened instead?
Phone is usually rings with significant delay

### Your phone model

Iphone 12

### Operating system version

iOS5.6

### Application version

v1.9.5

### Homeserver

https://matrix.sandsai.com/

### Will you send logs?

Yes