I am not at all sure what's going on here, whether this is chicken or egg, but...
I booted my Win 10 guest OS (it has many hours on it now, and has been very stable). Before the Win10 home screen appeared, the USB device detect popup appeared, inviting me to assign the device (a joystick) to OSX or Win10. I clicked on OSX (the default). But the USB popup window did not go away!
The USB assign window stayed up. I could not dismiss it. It stayed up on top of my OSX desktops, it stayed up on my Win 10 screen. It was impossible to access anything underneath the window, and impossible to move it. So neither OSX nor Windows was very usable with this obstruction front and centre.
Eventually I had to force-quit Parallels to make it go away (Parallels control centre was hung).
When I rebooted Parallels VM, I ended up in a seemingly eternal "deleting snapshot" hang, which I'm still waiting for. It's been maybe 10 minutes now.
What I don't know is whether it was the "delete snapshot" hang that caused the USB assign to hang, or whether my force-quitting of the app to get rid of the USB assign popup caused Parallels to revert to an earlier snapshot, or...? I'm fairly new to Parallels and have only the most shallow knowledge of the app (i.e. I can get it to run Windows on one of my desktops, but have no idea how the magic actually works).
If anyone has an idea as to what happened here and how to avoid it in future, I'd really appreciate a word of advice.
UPDATE: My Parallels VM is still unusable even though Snapshot Deletion has finally completed (after 15 minutes maybe?) -- I still have the USB Device Assignment popup, and when I try to click on it I get the beachball cursor and cannot interact with it.
prl_display_service is getting 120 pct of my cpu (a core and a bit), and Parallels Desktop is getting between 30 and 50 pct.
update 2: the pesky USB assign window finally went away (I unplugged the relevant device), but my VM is still very confused. when I try to switch to the vm desktop, it looks OK for about a second, then scrolls sideways to a further desktop with the wrong resolution and a distorted Win10 desktop image. I cannot stay on the good desktop -- it always slides me over to the bad one.
not sure what to do next! but at least the snapshot delete finally finished so I have some hope of sorting things out. this is the first time my parallels installation has done anything other than perfect, transparent functionality so it has been quite a shock.
final update: what I did to fix the bogus desktop. I used OSX Mission Control to "shrink" the bogus extra desktop to a screen window. Then I Quit that screen window. This left a correct copy of my VM on its desktop with the right screen rez, still running. I have no idea what happened there but if someone else has this problem, collapsing and quitting the extra instance of Win10 vm seems to fix it.
all I wanted was to fire up Windows to do a simple task, and now it's over an hour of head-banging later... whatever "deleting snapshot" is, it's bad news 
Last edited: Jan 28, 2018
