Sounds simply like caliper alignment to me. It should have lateral adjustment with the bolts slackened enough to clear the rotor but sometimes it’s a lot of faffing.
Have you done the loosen, apply brake and at the same time gently tighten each bolt one bit at a time, then spin to see if it clears? Also putting thin cards between rotor and pad and doing the same procedure can help.
And you’ve pushed the pistons back before doing all this?
Other thing is different caliper positioning, which could happen due to slight differences in forks, can mean the pad wear doesn’t match up to the position. Try new pads. Back of contact adjustment also if you have it on the brakes.
Other than that, double check the post mount is the same size. They are usually the same, but sometimes may not be I think.