I'm experiencing a really annoying freezes/hangs I've never seen before in OSX. Audio continues to play, but everything else freezes and never unfreezes. I can't even open the Force quit dialogue. Only way out is to hold the power button and then restart. Went back to El Capitan, all is fine. I tried again with 10.12.1, and it's doing it again. Like three times within 6 hours. Rolled back again. The usual dance of PRAM/SMC/permissions/reinstalling combo update didn't fix it. This is a 2015 5k iMac. AHT and memtest pass OK. Anyone else?