I got a problem with mixbox in FL21 on Windows10 (running at 48kHz): The De-Esser only works correctly in "soft" mode, in regular mode it produces a lot of crackling, and turning up the buffer size doesn't help.
I just got mixbox the other day, but everything else seemed to work fine so far.. I also got the de-esser as VST and part of TRacks, the VST works fine, too.