Why does this happen? It is because some comments are hidden by moderators/users? Because I'm actually happy to read every comment on images but sometimes there are little to no comments even after pressing the "Show all comments" button

The comment count on a post and the visible comment count are separated, hiding comments does not updated the former
So yes, it's hidden comments

donovan_dmc said:
The comment count on a post and the visible comment count are separated, hiding comments does not updated the latter
So yes, it's hidden comments

Ah gotcha, thanks for answering so fast!