This definitely isn't correct:
https://github.com/mybb/mybb/blob/featur...p#L926-927 Not sure what $visible is doing there when the next line assumes everything can be viewed...
And the whole block is not even available in forumdisplay.php = counts are not queried, which is the only big difference I noticed. For guests pages in that thread are always 1-7, which also suggests it's mod-related.
EDIT: and ofc this isn't correct when it comes to permissions:
https://github.com/mybb/mybb/blob/featur....php#L1118 but there's an issue for many similar cases already. The conditional doesn't make any sense either since it considers only unapproved posts while soft deleted are also added - that's likely the cause.