User presence accounting problems seeing all people in a room

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

### Background information

- **Git pull yesterday, so 0.8.9?**:
- **Monolith**:
- **SQLite3**:
- **No Docker**:
- **go version 1.17.7**:
- **Issue persists with any Client**:

### Description

- **What** is the problem:
- Users under settins/info "People" not showing all people, in element desktop showing self as offline, in android client those offline users not even listed at all, invisible
- **Who** is affected:
- Just about everyone using my Dendrite home server?
- **How** is this bug manifesting:
- "Manifesting" quite well for all my users
- **When** did this first appear:
- I think it first appeared from the "beginning" of my using matrix chat (i never used synapse)

### Steps to reproduce

Please see Issue Opened on Element-Desktop, but I thought it may be Dendrite issue since just about all clients are affected:
https://github.com/vector-im/element-web/issues/22955

Start by reviewing the linked Element Desktop issue and reproducing the missing-user and incorrect-offline presence across clients. Then inspect Dendrite's presence accounting and SQLite-backed behavior; done means all room members appear consistently and their online or offline status is correct.

Written by the indexing model from the issue text.