There is not enough information on this thread. It would be useful to take a screen shot when the issue is occuring. I am suspecting that when the "VMware Tools Core Service" keeps popping up on the UI, there is a chance that the service is crashing. When the issue is occuring, gather the Fusion logs. For more information, see Collecting diagnostic information for VMware Fusion (1003894) . Once gathered, share in the thread.
I'm guessing this could also be the new app in Fusion 10 that launches whenever you enter Unity, and displays a pseudo-start menu when clicked on.
I hope there's a way to disable it?
A little more time is needed for just entering into the unity mode.
It should stop popping up soon.