Unfortunately, I've had the pleasure of doing about dozen systems over the years, from varied manufacturers, ALL of them having similar obstacles to overcome. At this point, I would suggest that you take several steps back, to a controlled frame of reference.
I would start by checking all your wires for continuity; then your connectors for a good, solid grip. (Most of those factory provided round brass connectors, [if you're using them], can stand a little "pinch" to snug them up. Where you installed any crimp connectors, give them a "pull" test to make sure they're snug. Finally, compare your wiring to the supplied installation diagram, one more time.
Then, I would test each solenoid by itself, independently, disconnected from any links or connection to your lock assemblies, with any wiring to the other solenoid disconnected as well. If one solenoid is "flaky", swap it side for side, to see if the problem follows the solenoid, or not, which would possibly point to the system "brain", and or relays. NOTE: To answer your previous question, the solenoids don't like operating against any excess resistance.
If all above tests well, then it's back to looking at your mechanical linkage connections; I'd be looking particularly @ your "bell-crank" double-lever linkage on the one assembly.
I know that it's frustrating to trouble-shoot these systems; it's a tedious process.....