I recommend to keep it because you just got -8 but getting the rarest rating change in cf.

Nothing much can be done, it seems. Recalibrating ratings for an older contest can't retroactively rate/unrate people in later contests, it'd cause a lot of problems if they can

That's the unluckiest thing I've ever seen. At least your max is Master now

It's never a big deal. I believe that you'll back to Master and make it higher soon. Btw, having such a strange rating change is also kind of interesting, isn't it?

If you aren't stable master right now then you will come back down to div 2 and everything will be fine again.