Now there are massive blocking of Twitter accounts.
Most often, block accounts when you to use mass-following. Blocks is forever!
Also do not use hashtags #ICO #Cryptocurrency etc
Be careful!
UPD
Some accounts of my friends that have been blocked marked "forever" are now unlocked
But anyway, I think we need to be careful
I guess this all happened since twitter bounty had started. Some bounty hunters are making a lot of twitter accounts and spamming followers to join twitter bounties. That is why twitter became strict with mass-following and banned some accounts.