Quote from: DdmrDdmr on Today at 11:17:07 AM

Not exactly. It means that -91 net posts were "created". Net posts are: Created – deleted +/moved. It is also subject to forum reindexes, which may affect these counters (data is derived from forum official stats, comparing consecutive months).
Essentially, it means that there have been more posts deleted or moved from the Indonesian Altcoin board, than created.

Quote from: fillippone on Today at 11:21:31 AM

Yes, negative numbers means the total post count of a specific board has decreased compared to previous snapshot.
This can be due to a number of reasons, namely

Post deleted by user
Post deleted by moderator
Post moved to a different board

It is important to notice that whatever the cause, the posts that have beencdelted/moved, might have been posted earlier than the last period. I.e., regarding this specific issue, total post in June on that board might well be positive, but outnumbered by old post deletions by a moderator.

Edit: sorry, didn’t notice @ddmrddmr already answered

Thanks @DdmrDdmr @fillippone, I updated the merit activity and monthly post for Indonesian local board. It seem that an incident like this has happened before when I haven't updated monthly post activities and merit for local board or to be precise in July and August 2020. Of course, because the activity chart that I made only specializes on Indonesian local board, then -91 will make one upside down candle on the monthly chart. Again, thanks for the explanation.