@sdalmond    Are you networked?  I've had fits with updates too; I'm networked using a main computer as my "server".   I install the update there, then do a HARD reboot before installing on the workstations one by one.   Reboot each one after the install finishes.  VERY time consuming 😞

It's still temperamental as hell, but it seems to help. 

I did read an article about making sure each workstation has it's own separate ID (I think you F 10, then the workstation is listed, look for the number and make sure they all have unique numbers).  

I feel your pain, good luck.  I've grown to HATE Thursday afternoons.