Dendrite syncing broken after upgrade to 0.8.8

*This issue was originally created by [**@edocod1**](https://github.com/edocod1) at .*

### Background information

- **Dendrite version or git SHA**: 0.8.8 (though it happens on 0.8.9 too)
- **Monolith or Polylith?**: Monolith
- **SQLite3 or Postgres?**: Postgres
- **Running in Docker?**: No
- **`go version`**: go 1.17.18
- **Client used (if applicable)**: nheko, FluffyChat and element web

### Description

- **What** is the problem: Rooms stopped updating and i haven't been able to send new events to any room
- **Who** is affected: everybody on my own server
- **How** is this bug manifesting: all rooms appear frozen since the update, all sent messages disappear after a while, there are no useful errors in the logs (everything seems to work fine)
- **When** did this first appear: after upgrading to 0.8.8

### Steps to reproduce

- Update to 0.8.8
- ?????
- Dendrite syncing does not work anymore

I would write to the dendrite support room, but with my homeserver not working it is very hard to do so. This is not a "pls fix" request but more of a "hey how do i troubleshoot this?"

Start by reproducing the upgrade from Dendrite 0.8.8 on the reported Monolith/Postgres setup, using the listed clients and observing server logs during syncing and event sending. The issue is done when rooms update and sent events persist after the upgrade, with the failure or regression identified.

Written by the indexing model from the issue text.