Hello I have exactly the same problems and so far no help from Parallels. My system: Parallels 15.1.2 - iMac, MacOS Mojave, 3.1 GHz i5, 16 GB RAM, 1 TB Fusion Drive. For 4 months I have also started from an external SSD 1 TB. My only "bad" solution: I have now a external Samsung SSD 1000 GB increased, Windows.pvm copied to it and see there Windows starts in 22 sec and the entire Windows system environment runs so much better. But that can not be the solution and I want to control everything from the internal hard drive. But the error is definitely not on the installed Windows system.