I was having a problem… every once and a while when I tried to paste special using ALT-E-S-T, the box that would pop up had lost focus. I’d have to use my mouse to click into it.
It took a little digging to figure out that Google File Stream was stealing focus. I had no idea why though… and I couldn’t close File Stream.
For me, turning off “Show who is editing Office files, and share with other editors if I am editing” fixed the problem. It’s not a perfect solution, but better than needing to use the mouse on a regular basis.