Maybe they started scamming even before ban in forum, we can't know for sure, but I think they started doing that on darknet forums first.
We would have seen genuine scam accusations if this was the case, given that Yomix was heavily advertised in the forum. Mixers like cryptomixer would have issues some weeks, but we would immediately see brand-new accounts register in this forum and report about mixing huge sums of BTC and not getting them back.