sync v3 requests hang indefinetly

### Description

When making a sync v3 request—with or without timeouts, filters, etc.—Synapse hangs indefinitely until the gateway timeout of the reverse proxy is reached (which is set at about five minutes).

I am seemingly the only person this happens to on my home server though.

### Steps to reproduce

1. reach a mysterious account state
2. make a sync request
3. consistently time out

### Homeserver

ccc.ac

### Synapse Version

1.151.0

### Installation Method

Docker (matrixdotorg/synapse)

### Database

PostgreSQL

### Workers

Single process

### Platform

docker-compose in an LXC container

### Configuration

_No response_

### Relevant log output

```shell
n/a
```

### Anything else that would be useful to know?

The start of the sync failing coincides with a matrix-appservice-irc reset on a room I am in. I honestly have no idea if this could even be related though.