Sounds like you’re having fun Paul!!!
In my own investigations, I found another couple of sources for my particular set up:
1. Moonlite motorized focuser had, over the years, come slightly loose and required me to re-tighten the socket head cap screws that “locked” it in place on the OTA.
2. Brass compression ring was just biting on the edge of a recessed 2” camera adapter and this was causing a small amount of “rocking” as the OTA orientation changed with altitude.
As the temperature dropped from the start of a session where I hand tightened locking screws and clamps, I found that it made these two “faults” worse as the contraction of metal upon metal made things fractionally looser too.
I’m glad you’ve got to the bottom of your issues.
Cheers
Dennis