Search in upgraded encrypted rooms doesn't search pre-upgrade history

### Steps to reproduce

1. Create a private encrypted room (version 6)
2. Send message `foo`
3. Upgrade the room (version 9)
4. Search for `foo` in the new room (version 9)
5. Search for `foo` in the old room (version 6)

### What did you expect?

Search results across upgraded rooms.

### What happened?

Searches in (4) and (5) do not show any results:


Sometimes however (4) and/or (5) do show some search results.

### Operating system

Windows

### Application version

Element version: 1.9.0 Olm version: 3.2.3

### How did you install the app?

https://element.io/get-started

### Homeserver

phys.ethz.ch

### Have you submitted a rageshake?

Yes