there was one case which may be categorized as a roll back but it was mostly a group of nodes that went on an invalid chain. it happened in early years and it is referred to as the "overflow bug" where due to a bug a miner created a bigger than allowed number of new coins which made its block invalid and other miners built on top of that invalid block and created an invalid chain which had to be discarded.
in my personal opinion this can't be categorized as a "roll back" because those blocks were invalid.
Further update: Binance CEO Zhao said the company will not pursue a rollback of the bitcoin blockchain.
this is a lie that they spread to cover their embarrassment. they didn't stop pursuing rollback! they faced the reality that is is not possible to do so and every miner they tried to bribe laughed at their proposal.
I would argue this unexpected fork was a rollback.
edit caused a rollback to fix the issue.At the exact second the fork occurred no one knew which fork was 'bad' once it was determined which fork to kill off i would say that the voided fork was a rollbacked fork.
By definition if an unexpected fork happens either fork could be viable.
Since it is not a planned fork a discussion to decide which fork must happen and the voided fork along with any coins go by by
So people hit for coins in the 'bad' fork and the coins were later poofed into thin air.
It is not like the eth rollback but I would think it is still a rollback.
I would have to say the pool I was on at the time was on the good fork. I did not lose coins but others lost coins being on the bad fork.
It took more then 1 bad block to fix it. so more then 50 coins were disappeared . I am thinking it was 2013 when it happened.
I mined with bitminter and we got a boost since 30% of the network was on the wrong fork. I know we got multiple extra blocks at the time.