Timeline scrolling becomes “sticky” after jumping to unread.

### Steps to reproduce

1. Open a room that has ~20 or more unread messages (enough that it will back paginate and not be a live timeline)
2. Tap the jump to unread pill at the top
3. Scroll down to the bottom of the room manually (so you’re still on a non-live timeline)

### Outcome

#### What did you expect?
Scrolling to continue normally

#### What happened instead?
Just before reaching the bottom the scroll view becomes really difficult to interact with. Seems new to this release. Possibly worse in 1.8.18/19 but it still occurred in earlier versions.

(Tapping the return to bottom button fixes the issue)

### Your phone model

iPhone 12/13 Mini

### Operating system version

iOS 15.5

### Application version

1.8.19

### Homeserver

_No response_

### Will you send logs?

No

Reproduce on an iPhone using iOS 15.5 with a room containing about 20 unread messages. Start by examining the timeline behavior after jumping to unread and manually scrolling toward the bottom; done means scrolling remains normally interactive without needing the return-to-bottom button.

Written by the indexing model from the issue text.