Thanks for the photos! I can see that it appears you are placing the proxmark3 at the crux of the antenna trace at a 45 degree angle. Reads require much less power than writes so it is possible that you are able to get good reads but not enough power to properly write. Also the placement of the metal screw right at that corner could be really messing with the field at that exact spot.
I would do this to maximize your write power;
- remove the LF junk from the board with a T6 screwdriver
- exposing the HF trace antenna
- place the HF antenna down so that is perfectly perpendicular over your xM1, but avoid that crazy crossover spot where the traces dive under vias in the PCB
FYI, write commands have no validation built in so they will always “succeed”… just like writes to a hard drive in your computer, it’s just taking it on faith that the bits are actually changed.