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Is there any chance you're holding Ctrl when you press Space? The combination of Space + Ctrl activates the zoom tool, as a deliberate shortcut.
If not, could you be holding down Ctrl at some other point at a moment when the XD app loses focus? If so it's possible the app gets confused and thinks you still have Ctrl held down when you come back later. I can't get that to happen on my Windows machine though, so if this is the reason we should try to understand what steps on your computer are triggering it -- please let us know if you see any sort of pattern in when this starts happening.
Actually, I've seen that it's happening when I press alt+space. And as I use alt for zooming and space for moving, I alternate very oftenly between the two and sometimes I press them both.
What it does is it opens the contextual menu of the application (it does this also in the other Adobe softwares, I think). And this messes up the behavior of the mouse.