I think the issues may actually be related. It appears to start with the error while monitoring VC task updates. Cloning fails and provisioning is disabled based on the setting to disable on error. After a while, Horizon attempts a recovery operation where it attempts to remove the suspect machine but fails- But tries to re-clone the machine only to see that the VM is still in vCenter.
One of my colleagues found that we had some duplicate folder names within our VSAN datastore that appear to be the root cause of the cloning issues. After restarting provisioning, a new folder for the problem VM is created with a "_1" appended to it and allows things to proceed. We deleted the original folders and everything has been running clean/smooth.
I suspect that these folders were lost/locked during a vCenter reboot at some point but will keep an eye out for them moving forward.
There was a bug that was fixed in 7.5.2/7.7 that addressed folders not getting cleaned up when a linked clones was deleted. We had to manually clean these up almost daily to avoid the extra folders with a "_1", "_2", etc...