It should be pretty easy to figure out at what nonce the server seed was changed (just work backwards until the bets doen't verify). And if the site has the original server seed then the bets before that nonce could be verified, which would make sure that the server seed change wasn't hiding unfair bets (that's assuming that unibtc was betting in a reasonably difficult to predict manner) and that it was just a silly mistake  =)


Or even if the site doesn't have the original server seed (which is a concerning red flag), it would still make sense to verify as many of the last bets as possible using the latest server seed and check if a losing streak fell under the latest server seed. If the losing streak happened to fall on unverifiable period, that would be another red flag.


(Although to be honest, I suspect the whole thing is just a silly mistake but the whole point of provably fair is that we can verify not trust)