That's it in a nutshell. There was a bug in the code, but the error was negligible under the loads Lemmy was used to, but the extra workload of thousands of extra users made the bug go from "fixes itself faster than I can blink" to "posts are still rolling in minutes later".

Luckily the inefficient code has been replaced with more efficient code and will be rolled out with the next major version. I personally don't know when that version will be released or how long it will take to deploy to the Lemmy servers.

At the end of the day though, I'd rather suffer the growing pains of someone trying to build something, than suffer the greed of someone trying to consolidate power.