I have oVirt 4.4.6 running on my Engine VM.
I also have oVirt 4.4.6 on one of my hosts.

The other two hosts are still on oVirt 4.4.5.

My issue seems slightly different than the issue(s) other people have described.

I'm on RHEL 8 hosts.

My Engine VM is running fine on the upgraded host, as is one of my Ubuntu guests.
However, it seems like I'm not able to migrate *ANY* other guests over the new host. 

The oVirt UI just indicates that for whatever reason the upgraded host isn't available / compatible for a VM to be migrated to.

I'm not sure how or why this 1 Ubuntu guest VM was able to get migrated, but it looks like its working just fine.

I did try:

yum downgrade edk2-ovmf

Base on other people's comments. But I'm not sure how long to wait, or what else to try, to try to get my upgraded host operational again.