This happened because of two main reasons:
1) Buying (let's say) 5000 mentions, you involve more or less 20k-25k users who don't give a fuck about your pic. Moreover, they've been tagged by weird arabic people 90% of the times. It's normal to think that at least 250-500 users reported the pic and blocked you.
2) Instagram alghorithms are the same who mass-delete accounts from the same IP if you don't cloak it properly with a good proxy...... they are obviously able to detect if a user receives 5000 comments in 2 hours.
This said, as mention is still one of the best way to boost traffic, you can't just get rid of them. You have to ask your mentions provider to split them in a couple of days. If he's too lazy, just buy mentions 500-1000 per order and split them in more pics.