Are you working up and down stream from where you are seeing the issue with your back?
Where you see the issue isn’t always where it originates.

The issue clears up until you reach the tolerance of your tissues again. The cause of the issue is still there.
Resolving the cause or where issue originates will resolve the issue for good.

Movement is key. Active recovery gets the body moving without stress on joints, muscles, and tissues.
Non exercise movement throughout the day makes a big different.

Beginning to use orthotics again changes things at the foundation. Foot position is different from what is has been. You could be making upstream compensations/adjustments to positioning which you may not be aware you are making.

What is your position like when you are in the kneeling desk?