I stumbled upon an unusual issue where I was unable to move objects in the top or front views, but I could move them in the perspective and right view. I Switching to single viewport mode didn’t help. The top and front views seemed like they were read-only. The only action that seemed to work was object deletion. This drove me bonkers for a while until I was able to “fix” the issue. I set each malfunctioning view to another perspective, then switched it back. That action seemed to restore normal functionality.
Rhino for Mac 5.5.1 (5F82)