Acrobat DC comments slow to open (Mac)

Of course everything is all up to date. I had already ruled out a user account issue since I see this behavior on both of the production machines I use regularly. I had also already tried deleting preferences (quite a few more than just the ones mentioned in your link) without success. So I was grumbling under my breath as I begrudgingly followed your suggestion of creating another user account. The problem seems to be gone! ...or, at least minimized. There's still an annoying lag of 2–3 seconds to open the commenting pane every time I open a file, but not the downright unusable lag of 15 seconds I was facing hundreds of times a day.

I wish I knew what the root of the problem is, though. There must be some other, non-obvious, preference file or support file somewhere in that User Library folder. If I knew which it was, I wouldn't have to lose hours of productivity recreating and rebuilding my user accounts on both machines.