I have experienced the exact same problem. Everything was running smoothly until I upgraded to 10.14.4 and now my VM is practically unusable as it's so slow and the CPU is constantly maxing out. Have tried re-installing the combo update and have run the Utility First Aid, but nothing has fixed the issue.
[Update#1] - I abandoned using my VM but left it running in the background for the past few hours and used apps on my iMac to work around the issue. Have gone back to the VM and whilst it is a little slow, it's nowhere as bad. Someone on this thread questioned if some sort of auto-optimization was occurring, and I'm wondering if that was the reason for the slow down and by letting it run it's course, it might just fix itself? Will leave the VM running for another couple of hours before shutting it down to see if that improves things.
[Update#2] - restarted my VM this morning, thought it was ok but no, it was practically unresponsive. Shutdown the VM, switched the hypervisor to Apple and switched off adaptive-hypervisor and for me (iMac 5K 27" i7, Late 2014) it solved the problem. Haven't played around to see if both actions are needed, or just one of them ).
Last edited: Mar 29, 2019