In this post, it's showing 6 comments, but l could read only 4. Moreover, it's my community, so I need to understand what's exactly wrong with.

I see this happen all the time and I presumed until now that it's due to my personally blocked users or instances being hidden from me.

The other comments probably come from cross-posts

I see number 4, with 2 top-level comments on quokk.au (the ones from feddit.online are missing, same as all posts in https://piefed.zip/c/news_from_the_subcontinent@feddit.online for some reason). Counting all the comments - the deleted one gives 4

I see that lemmy.ml is blocked on feddit.online, so that explains why you don't see that other comment

If you count all the comments and subtract the deleted one, there are 6 comments under your post on feddit.online ATM

Looks like it's the combined total of both your post in news about the subcontinent and world news@quokk.au. There's 3 comments in the one community and 3 in the other one, plus a deleted comment. That makes 6.

But PieFed had issues with the number of comments calculation before. As far as I remember on occasion it'll do the maths some other/wrong(?) way. So this number might be inaccurate.