Scrolling up in a specific room makes recent messages disappear

### Steps to reproduce

In the Matrix Foundation room (#foundation-office:matrix.org) whenever I scroll up past a certain point element-web "flashes" momentarily and then recent messages disappear from the timeline. Attached is a video demoing this.

https://github.com/vector-im/element-web/assets/1254842/81876396-b5e6-4c9d-965e-2ee9e3c41d98

The "flash" happens around 0:04-0:05.

### Outcome

This persists across refreshes and even persisted across an upgrade from v1.11.47 to v1.11.48. I haven't tried a "clear cache and reload" since I suspect it might fix the issue and it might be useful for debugging. I can only reproduce this in my desktop and not my laptop with the same setup (matrix account, same firefox version and plugins).

### Operating system

Debian Bookworm (12)

### Browser information

Firefox ESR 115.4.0esr (64-bit)

### URL for webapp

https://riot.dgrig.com

### Application version

Element Web 1.11.48 (but happened in 1.11.47 too)

### Homeserver

Synapse 1.96.0~rc1+bullseye1

### Will you send logs?

No

Start by reproducing the timeline failure in #foundation-office:matrix.org using Element Web 1.11.48, Firefox ESR 115.4.0esr, and Debian 12, then compare the desktop and laptop setups. Review the attached video around 0:04–0:05 and gather logs or other debugging data; done means scrolling up no longer makes recent messages disappear and the behavior is understood across refreshes.

Written by the indexing model from the issue text.