Cannot edit meshes anymore after some time

[clemlak]

This issue appears almost every time: I can create, place and edit meshes (except the ramp that doesn't work), but after a while, for example a couple of hours, I cannot edit the meshes anymore.

The following error appears in the console:

 res://addons/onyx/nodes/onyx/onyx_gen_box.gd:693 - Invalid operands 'Nil' and 'Nil' in operator '-'.
 res://addons/onyx/nodes/onyx/onyx_gen_box.gd:693 - Invalid operands 'Nil' and 'Nil' in operator '-'.