Same issue here. Just cropped up in the past few weeks. The reset position button doesn't seem to fix things. I can (temporarily) fix it by either:
1 - Forcing a reload/re-import of the .sensorpanel file for my layout.
or
2 - Disconnecting the monitor, rebooting and then repositioning the panel once it reappears on the main monitor.
The issue crops up again intermittently. I fixed it a week or so ago and it just cropped up again today.
Has anyone found a more permanent fix for this?