I can reassure you, you are not alone. I think I know what you are talking about (Windows 10).
A few days ago, I switched my video driver from OpenGL to ANGLE, which seemed to fix a RAM usage problem I and other Windows users had:
The switch helped in some ways, but I still get inexplicable performance drops from time to time, especially when editing card templates. Loading the preview for a card takes a few seconds now, whereas before it was much more snappy, almost instantaneous.
I noticed the input lag you’re talking about, too. Whenever this happens, I restart Anki (old habit, used to it from the previous RAM issue anyway).
The problem is kind of hard to pinpoint down, since I have a large add-on collection. If I find a way to replicate the problem reliably without add-ons, I’ll post it here.
[got a hellweek at uni right now, my testing will have to wait until next weekend]