Trashcan Mac Pro (2013) 6-Core, AMD FirePro D500 Graphics, OS X Sierra 10.12.6
Same GUI lag that was present in 12.8.2 - seems to come and go at times - most noticeable when zoomed in a few levels on the edit view. Sometimes helps to close and re-open session/application, other times does not. No background activities consuming system resources aside from PT. Lag unnoticeable when zoomed out enough levels.