I installed rhino 9 WIP so I could check if this is still present and sadly it is
It is bug that one of us described in topic below and even shows video of the problem.
When u have proporties tab open and choose new object in the scene then u have “a freeze” or a “lag” - very very annoying. It makes us turn off properties tab to make rhino work properly or lose our minds dealing with “a lag or a freeze”.
The model does not matter, it is still present in new scene with a single box. same issue.