Other people's session list doesn't update under sliding sync

### Steps to reproduce

1. Element Nightly, turn on Sliding Sync
2. Go to an encrypted room

It's unclear whether the combination with Rust Crypto causes it

### Outcome

#### What did you expect?

For each member, the correct list of sessions are displayed

#### What happened instead?

Some members' session lists are not updated at all, therefore:

* messages they sent from those sessions are marked with red warnings ("unknown or deleted device") on my client, and
* they cannot decrypt my messages from those sessions (UTD)

### Operating system

macOS

### Application version

I'm on Nightly and I update daily. This issue occured in the past week as well as several months ago.

### How did you install the app?

official page

### Homeserver

tchncs.de

### Will you send logs?

No