Thank you, your solution using quota disable and enable worked!
Rescan run for about 30s but didn’t fix the issue. Gparted live cd and Tumebleweed live cd still gave the same errors.
nbd@nbd-x300:~> sudo btrfs quota rescan -w /
[sudo] password for root:
quota rescan started
nbd@nbd-x300:~>
Following you second solution, I used quota disable command, enable, disable again (I wasn’t sure what’s the proper order of things). Then I booted into gparted live cd and moving and resizing went smoothly. System booted normally without issues. Lastly, I used quota enable command again. Now I enjoy extra 100 GB on / partition.
Thank you again!