!.) Check the Service Bulletins here:
LulzBot TAZ 6, Frame Squaring, Service Bulletin
See if you have one of the affected serial numbers
2.) Here’s a link to the physical frame squaring check procedure:
If you were to disconnect the load on the Z-axis by disconnecting couplers that ride on the Z-axis rods and were to turn one of the rods you would see the other rod move up or down in parallel with the one that you are turning, so yes they are synched together. Therefore if you’re going to try and level the two disconnect the wiring harness from one of them and then adjust until they’re level in respect to each other, if you don’t I think it goes back to the same position, thus remains out of synch.
Personally I find the tape measure method difficult when you’re dealing with millimeters trying to get them as close to the same as possible between each other. Lay a strip of wood or something strong and flat that you can get on the couplers and put a level on that strip, then adjust accordingly until the level reads level, then reconnect the wiring harness.
When I first got my Taz 6 mine got out of alignment somehow until eventually one of the couplers cracked. I returned it under warranty for repair and lost a lot of $$$ in the shipping cost. That’s what they found, a cracked coupler. I learned! Hope this info helps you and others like it did me.