I'm not sure if this is a plugin topic or theme topic...
I've followed your steps to update a test site to 6.0.4 and have a few errors showing up as follows:
1 - At the top of the Forum dashboard, I'm getting an error "Either the tablet theme css file and/or color overlay file from the selected tablet theme is missing". I can't see any problem at the front end but also can't get the message dismissed. I have Reboot child framework, 2.0 active and have tried deactivating and reinstalling but still get the error. Same if I switch to Reboot 2.0
2. There are two 'pink' errors flagged up in the Toolbox>Error Log: (screenshot)
PM system seems to be working ok
Thanks for any suggestions.