More timeline improvements; Bug fixes.
Interesting. I have not personally noticed the slight freeze time when performing Undo action. I usually use the "CTRL + Z" keyboard shortcut, all applications have.
Sometimes I will Undo several changes in rapid succession as well. Have you tested standard web browser troubleshooting. Clearing all cache/cookies/etc? Or test in other browsers?
I used to work at a very large pharmacy in the States, in the Corporate IT Support Dept. For most web apps, I would just remote into their computer, and run through standard web browser troubleshooting real quick. And, the web apps would restore their normal behavior.
If that doesn't help. It might be something else, between the differences of our two machines. If other folks are experiencing this as well. I wonder if it could be tracked down to a specific piece of hardware/software in all machines affected.