I am running Windows 11 on PD18 in coherence mode. Periodically throughout the day, a large gray box will show up for about 10-30 seconds covering the left half my desktop. It looks and feels like parallels is trying to show a window, but nothing is shown. When I switch out of coherence, the box goes away. Is there any guidance as to what could be causing this? It seems to have started all of a sudden - without a change to my parallels configuration, installed version, or windows configuration.