I have a similar problem with ChimeraX 1.11.1 on Windows 11. Unable to restore session, resetting. Traceback (most recent call last): File "C:\Program Files\ChimeraX 1.11.1\bin\Lib\site-packages\chimerax\core\session.py", line 863, in restore obj = sm.restore_snapshot(self, data) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "C:\Users\a\AppData\Local\UCSF\ChimeraX\1.11\Python311\site-packages\chimerax\artiax\particle\ParticleList.py", line 1232, in restore_snapshot pl.collection_model.displayed_child_positions = copy(pl._displayed_particles) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "C:\Program Files\ChimeraX 1.11.1\bin\Lib\site-packages\chimerax\graphics\drawing.py", line 266, in __setattr__ super(Drawing, self).__setattr__(key, value) File "C:\Users\a\AppData\Local\UCSF\ChimeraX\1.11\Python311\site-packages\chimerax\artiax\particle\SurfaceCollectionModel.py", line 292, in displayed_child_positions col.display_positions = copy(value) ^^^^^^^^^^^^^^^^^^^^^ File "C:\Program Files\ChimeraX 1.11.1\bin\Lib\site-packages\chimerax\graphics\drawing.py", line 266, in __setattr__ super(Drawing, self).__setattr__(key, value) File "C:\Program Files\ChimeraX 1.11.1\bin\Lib\site-packages\chimerax\graphics\drawing.py", line 418, in set_display_positions self._any_displayed_positions = (position_mask.sum() > 0) ^^^^^^^^^^^^^^^^^^^^^^^ TypeError: '>' not supported between instances of 'NoneType' and 'int'