Thanks for the information provided to the Illustrator team.
We are able to reproduce this issue at our end and the engineering team is currently isolating this issue further to get to the root cause.
With Best Regards,
An error occurred while saving the commentClint commented
Happend to me in April, 2019. I running a 2017 15" MacBook Pro (16gb Ram). Never had an issue until I tried using the Duet app with my iPad pro. When I did that, the handtool was the only thing that would work on Illustrator. I tried unplugging the ipad, didn't fix it. I quit Duet and force quite anything running in the background associated with Duet, still didn't fix it. I had to restart my computer to getit to work. I made the changes I needed, connected the ipad back up with duet and the problem came back.