Aggressive jumping around when scrolling through old messages

[y-decimal]

Describe the bug

Scrolling old messages on mobile PWA randomly jumps to different points in history.

ScreenRecording_02-26-2026.16-37-23_1.mov

Reproduction

1. Open any chat with a long message history
2. Scroll up a fair amount (for example to the first unread message in an active chat)
3. Start reading the messages from oldest to newest, scrolling down in the process
4. At a seemingly random point (possibly related to the loading of messages) the chat will jump aggressively, leaving you at a completely different point in the message history

Expected behavior

Normal scrolling with no jumping

Platform and versions

OS: iOS
Browser: Safari PWA
Version: 1.1.7
Homeserver: Matrix.org

Additional context

No response

[dozro]

experiencing the same

[Just-Insane]

There is a stop-gap fix for this in #279, however, as mentioned, a rewrite of how we handle timelines via #175 would be a lot better.