On an A back, the counter should reset when you take the insert out, and should stop at 1 when the winder stops. But, it doesn’t take much when you are lining up arrows to throw things off, 1/8th of an inch too far or not far enough is sufficient.
If the back reset correctly and stopped correctly for frame 1, and you lined up the arrows, then the back likely needs a CLA.
Another possibility could be not winding the back to frame one and just shooting. Are you missing any shots you remember making but are not on the roll? (i.e. got exposed on the paper ahead of the film). It’s an easy mistake to make when you’re in a hurry, DAMHIK.