BR1 MK2 not recognizing SIM after 8.3 f/w upgrade

BR1 MK2 ran fine on f/w rev 8.1 and brand new SIM.

Downloaded file and updated to 8.3 via PC last evening and now the cell side is stuck on “obtaining IP address” and when I dig a bit deeper it shows no SIM detected in slot A or B.

Updated f/w again to 8.3 but this time using the ability from “inside” the router itself. No change.

Re&re’d the SIM several times, verified correct physical orientation - all good.
Re-booted (power down/up) several times. No change.
Let it run overnight - no change.

help?

Thanks

Swapped the SIM to slot B and up she came - all good now

Weird