and then straight back to the resistance and this would get repeating itself. So not sure how it know where to start the magnets in position.
Are you saying that on one cycle of switching the magnets travelled to and fro several times?
It seems normal for the magnets to motor to about 1/2 inch in on turbo switch on.
If you switch it off and on again the magnets will cycle back to the mini position then back to the 1/3 inch position, I assume that this is a BIT (built in test) cycle to confirm the stepper is working and the magnets are not stuck on the mini stop.
When you join a session they will motor back to the min stop.
If the magnets keep cycling it could bee failing the BIT but I can't think why if its not getting jammed on the min stop.
What has been seen by others is when the magnets get close to the conductive ring on the flywheel they don't move back because either the thread is worn or the stepper is too weak to overcome the magnetic force but yours seem to be working fine.
Trying to use the Trainer on another a system seems a good idea or you could try the new BKool phone app which runs basic interval sessions and the like direct with the trainers sans internet connection.
One stupid thing is to make sure the trainer is paired still, especially if you have a cadence sensor as it might be assuming you have a dumb trainer.