Spent the time tonight to track down why Automation (copy/pasting) has not been working on both of my Macs; Divided Track List is the culprit.
Coming at it from every possible angle (including trashing prefs), the common denominator is soon after DTL is activated. Try it for yourself to confirm.
Simple recipe:
1.) Create empty session
2.) Make sure DTL is off
3.) create any number of tracks (in my case I tried FX and Inst. tracks)
4.) mouse-create a bunch of Vol automation data on one track
5.) start copy/pasting all over the place (use all possible selection/positional methods)
ALL GOOD SO FAR
6.) activate DTL (in my case it did not matter that I repositioned any tracks into the upper area or not)
7.) continue copy/pasting
8.) at some “fairly immediate” point, the pasting will stop working.
Related, DTL causes other strange behavior, as the forum clearly catalogues.