You don’t elaborate whether device has been in use with both SIM slots occupied and just renewed one SIM and found slot 2 not working, or been using one SIM in slot 1 all along and just thought to try slot 2 now with replacement SIM. Do any of the gold pins in slot 2 look at all distorted compared with slot 1?
Is your new SIM a three in one and you have pushed out microSIM size with nano inset or is it dedicated microSIM? Newer type of SIM holder in FP2 exerts more contact pressure upon the thinner nanoSIM portion in centre as here:https://forum.fairphone.com/t/fp2-microsim-adapter-broke-sim-card-slot-pin/12225/26?u=aspergerguy