Threads listed as unread when joining a new room

### Steps to reproduce

1. I'm fairly new here. I joined https://app.element.io/#/room/#SocialCoop:matrix.org
2. I noticed that the Threads icon in the upper right has a dot next to it, which suggests that there are unreads/notifications.
3. I click it and I'm surprised to see lots of unreads - I think "surely these haven't happened in the few minutes since I joined the room?!"
4. I can clear the notifications, but I would expect it to be clear when I join a new room.

### Outcome

#### What did you expect?

I would expect thread notifications to be listed as read when I join a new room.

#### What happened instead?

There were lots of thread messages marked as unread.

### Operating system

Linux Ubuntu

### Browser information

Firefox 138.0, Mozilla Firefox Snap for Ubuntu, canonical-002 - 1.0

### URL for webapp

https://app.element.io/#/room/#SocialCoop:matrix.org

### Application version

Element version: 1.11.100 Crypto version: Rust SDK 0.10.0 (3cc301d), Vodozemac 0.9.0

### Homeserver

matrix.org

### Will you send logs?

Yes