The 'jump to unread' button doesn't work most of the time

### Steps to reproduce

1. Open a room where you have lots of unread messages
2. Press 'jump to unread'
3. Watch it fail to jump
4. goto 2

### Outcome

#### What did you expect?

'Jump to unread' should work on the first try.

#### What happened instead?

Most of the time it appears to perform some kind of jump, but maybe not to the right place, and then the timeline somehow snaps you back down to the bottom, negating the jump entirely. I also get a bunch of 'job cancelled' toasts when doing this.

https://user-images.githubusercontent.com/48614497/177043105-00afa79f-1686-466d-bd8b-4cd045ab2fdb.mp4

### Your phone model

Pixel 3a

### Operating system version

LineageOS 19 (Android 12)

### Application version and app store

1.4.20 from F-Droid

### Homeserver

Synapse 1.61.0

### Will you send logs?

No

### Are you willing to provide a PR?

No