Thanks for using
Notezilla .
It happens if we hold the Filter or Memoboards pane in the top area and drag it at different location. It could have happened accidentally.
1. Exit
Notezilla
2. Run the below command from the Run window (press Win+R to open the run window).
"C:\Program Files\Conceptworld\Notezilla\Notezilla.exe" /ResetLayouts
This should reset the filters pane.