GreXXL Sorry for the late reply, unfortunately it's a private forum so the owner isn't keen on giving external access (I'm just helping with the technical/backend stuff).
I'm not sure how to reproduce it, this is an old forum migrated from an ancient phpBB, we have around 10k discussions and more than 1 million posts, an user randomly noticed this issue because one discussion had seemingly disappeared from the list but was quickly found using the internal search. Turned out it was the first discussion that should have been loaded with the "load more" button but it was skipped, and by monitoring I noticed this is consistent.
I'll try to reproduce it with a fresh installation and get back to you, thank you. Maybe I can clone everything, purge every discussion and see if the problem persists, that way I could let you in to check.
