I've also upgraded to 3.0.0.21 and am experiencing the exact same issue.
The VNC remote control works fine, then all of a sudden it just stops displaying on my side, although the end user can see my mouse still moving.
I've also noticed that when it stops displaying on my end, if I close the session it does not remove the process/service on the remote end, and I am therefore unable to use Lansweeper remote again until the PC is reboot and/or the service is manually removed.
It would be great if anyone had any feedback on this as I would like to use Lansweeper remote more.