Does the patch staging works fine?
can you upload the vum logs from VCSA? it will have the details on failure.
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I have run into the same issue few times now on two hosts. VMware support was not able to find much. Have you tried updating one host through CLI? In my case, I was able to update using CLI. And since then the same hosts are successfully updating through VUM. Mine is 6.0 environment.
What storage medium are you running ESXi on, as in is the hypervisor on local disks or on a USB drive? I ran into the same error trying to install the latest patches, and after speaking with vmaware and checking the esxupdate.log and vmkernel.log we were seeing (in my case USB drives) drop offline and the installations stall/failed
Update manager error 30 is if the ESXi cannot see the /bootbank
check the vmkernel log if the bootbank is not loaded messages or bootbank missing etc
you can try to browser cd /bootbank and check if that is working