Likqez there are some edge cases where the counters are not updated by Flarum. Most of these are reported on the GitHub tracker and I believe a lot were fixed. This might affect deleted posts or discussions.
Also it's possible it counts some discussions that are not publicly visible ? Maybe a private discussion or in a hidden tag ?
If you find what lead to the inconsistency, let us know so we can check whether it's a known issue.
