We did change a lot of door lock a few years back.
I had one VZ ute that I replaced the RH door lock first, and it didn't work,
then I proved the BCM (Body Control Module) was faulty, fit new BCM and keys, then replace BOTH front door locks again.
The faulty BCM blew up the door locks as soon as they were plugged in.
Yours does sound like door lock/snib issues.
I would start at the LHF door, since it is the 2nd most important door.
More than likely, replace the door lock.
Still available from Holden.
Ensure the snib button rod is straight and not causing any unwanted side loading of the snib button on reassembly.
By your description, the RHF is ok.