Messages no longer syncing properly

#### Description

Messages will sporadically not sync, until I close element-desktop entirely and restart it. At the beginning, messages are consistent (including with my other Android session) and then they diverge for Desktop, with approx 50% of messages not appearing, across any chat. Probably related to #17966 since I get that too, and sync being dodgy in general. The error that keeps repeating is this (sending rageshake too):

```
2021-07-13T08:52:44.317Z E Caught /sync error TypeError: Cannot read property 'roomId' of null
at Object._evaluateEvent (vector://vector/webapp/bundles/5b667ec9b5ae6c11f354/vendors~init.js:2:798461)
at Object.onEvent (vector://vector/webapp/bundles/5b667ec9b5ae6c11f354/vendors~init.js:2:797853)
at z.s.emit (vector://vector/webapp/bundles/5b667ec9b5ae6c11f354/vendors~init.js:2:19261)
at vector://vector/webapp/bundles/5b667ec9b5ae6c11f354/vendors~init.js:2:3531171
at Array.forEach ()
at p._processSyncResponse (vector://vector/webapp/bundles/5b667ec9b5ae6c11f354/vendors~init.js:2:3531021)
at p._sync (vector://vector/webapp/bundles/5b667ec9b5ae6c11f354/vendors~init.js:2:3529101)
```

Any advice much appreciated!

#### Steps to reproduce

- Be me
- Use element

#### Version information

- **Platform**: Desktop

For the desktop app:

- **OS**: Ubuntu 20.04.2
- **Version**: 1.7.32