This is a known issue. Will be fixed by adding a who-cache to soju, WIP patch here: https://git.sr.ht/~emersion/soju/commit/de704e4b53bcd078569a88a618ade51b19b0779d
This is not a serious bug, the main consequnce is that channel members could appear as being there even though they are away.
Keeping the ticket open until this is merged on soju's side.
In my case it was very serious, it made the client effectively unusable. I was flooded with error messages, and some combination of rate limits and connection overload made it difficult to chat at all (even in the #senpai channel).
Here is a short log of the errors in soju: https://paste.sr.ht/~techcable/a51f52f9273bc0964320deb201037f3fc148ce31
The following patch (to senpai) "fixed" the issue and by completely disabling WHO requests for
Since applying that patch to my client, senpai has been working flawlessly ;)