Hi,
I tested the 13.6.1 patch with one of my heavy projects (including Raytraced-3D , Element 3D etc) and the problems are gone. Undo worked and the viewport is responsive now.
However, there are a few things that I would like to point out :
1) When I opened the project file, the viewport seemed to struggle to show the visuals for about 10 -15 seconds.
2) When a preview plays (after rendering is done), the audio comes with a huge delay. Only after it repeats the preview, I can hear the audio properly (synced with visuals). Previous versions of after effects didn't have this problem.
3) After effects crashed (in minimized) when I was getting a preview and working with Chrome at the same time.
Hope this helps!
Tested on :
MacBook Pro i7 4870HQ 2.5 GHZ (2015 model)
AMD Radeon R9 M370X
16 GB Ram
Windows 10 64bit (Bootcamp)