I can’t change the show settings in my document anymore.
Tried on mimo 5.8 and also 5.9 beta.
If I create a new document then all is fine, but on my existing document it doesn’t work.
You can’t change the show settings when there is an output destination that’s live. Check that all output destinations are off and try again.
got it! I had a blackmagic output that was active when it was supposed to be switched off 
thanks