The usual, just changing the wheel set on my bike this morning for a ride about now , both wheels sets have 160mm disc rotors.
I take off the wheels with a six bolt Ashima rotor off (f&r) and I am trying a wheelset I have not used on this bike before which has a 160mm centerlock disc fitted on the rear and the wheel it no go round!
Seems like the disc is bigger? Both 160mm
What do I need to know!

where is it catching?

The outer edge (the thin cross section not the braking surface) of the disc is rubbing on the caliper

Well the simple way to check is lay both together and see what the difference it but maybe adjust the caliper?

Yep,
I will put the other wheelset back on today.
I did want to try the set of Scwalbe spiky tyres on the other wheels before the weather changes- they have been hung up in the back of the shed for about 4 years .One of those things you buy in a sale!

Perhaps put thin washers under the caliper to lift it slightly.

Is it a rear spacing issue?
Some frames will maybe accept an under or overwidth hub but the caliper will def not be happy?

i always have to adjust the brakes when I swap over my wheels – nit by much mind but i do have to adjust

Almost always have to do calliper alignment when swapping about, but if the edge (rim?) of the disc is rubbing then sounds like the spacing isn’t right or an issue with the new rotor.

If it was braking surface rub, then it’s simply alignment job (which I spend ages trying to get right and sometimes end up getting the adjustable spanner out to bend the disc until it stops 😀 . It’s been worse since SRAM moved away from CPS washers).

What’s the rotor? I’ve read issues with some, like Hope for example, if not used with their own brand brakes.

What calipers?

I’d guess that the Ashima rotors are slightly under 160mm. In fact you might even have an unswept area on the pads. Have you had a look at them?