VoIP: answering incoming calls only reliably works when accepting in notifications, but not in-app

**Describe the bug**
When there is an incoming 1-on-1 call, accepting the call from the Element app rarely (if ever) works. But accepting the call from the notifications works.

**To Reproduce**
Steps to reproduce the behavior:
1. Wait for a 1-on-1 phone call.
2. Try to accept in the Element app: it does not work.
3. Now try to accept from the notification: it should work right away.

**Expected behavior**
Incoming calls should initiate correctly from in-app as they do from the notifications.

**Smartphone (please complete the following information):**
- Device: Huawei P10
- OS: Android 9

**Additional context**
- App version and store: 1.0.17 [40100172] (G-b1275) - Google Play Store
- Homeserver: matrix.org