I have a problem with a windows machine where this error always pops up. The user that is supposed to be using (blocking) tailscale is not logged in and also not using it, it is an admin user that is currently not used.
Uninstalling tailscale does not help.
There are no other people logged in, that is the bug. I’m the only person that uses the other account and it is a admin account that I only use while setting up the machine, it has been rebooted many times since then, I’m positively not logged in.