I’ve had the same problem on Premiere 2017.2 with the beachball of death, whenever switching between timeline tools. I have just upgraded to 2018 and the problem is still there. Hugely upset right now. FML. Please let me know if anyone solves this! My audio also cuts out when I make changes during playback…which was one of the best features Premiere had…until it stopped working.
Just trashed all my prefs to see if it helps. Will keep you all posted!
Mac OS 10.12.6
Mac Pro (Late 2013)
3.5GHz 6-Core Intel Xeon E5
64 GB 1866 MHz DDR3
AMD FirePro D500 3072 MB