Can you try this?
1) Take photo from the drive side of the frame. Measure how far the through axle is from being flush to the nut / how far in the TA is.
2) Repeat without wheel but thread the axle all the way in. If there is no difference you can be sure the through axle is just wrong size.
In any case you could measure the through axle dimensions. Length from the base to the end. And length of threaded area.
Thanks for this. I did some measurements:
1. When fully tightened to 10NM with the wheel on, the through axle is not flush to the end of the nut/cap on the drive side. It's about 6mm short of flush. When I removed the wheel and inserted the through axle, it's around the same 6mm short of flush.
2. I took measurements of the through axle and the rear drop out area.
Does this help to diagnose the problem?