Silicon lottery is rare in today's CPUs. All mid range CPUs will have no problems with 3600 speeds, it's only when you play with the timings and subtimings that the IMC gets stressed with. XMP will work on single channel as well, you'll get a performance uplift depending on the workload with dual channel but stability will not be compromised in both cases.
3200 Mt/s is stock speeds for the i5 12400F without XMP enabled. It can do over that with a B or Z series motherboard.
OP, I'd suggest changing the position of the RAM stick in different slots as mentioned above. I highly doubt if that would change much, and if it doesn't, RMAing the DIMM would be the only option.
Edit: if 3200 works fine, then I'd say leave it. Getting another 16GB stick would be ideal though.
3200 Mt/s is stock speeds for the i5 12400F without XMP enabled. It can do over that with a B or Z series motherboard.
Edit: if 3200 works fine, then I'd say leave it. Getting another 16GB stick would be ideal though.