Hi, @Brenton_Gray.
If it’s of any use, we faced a somewhat similar problem using the RAK831 gateway with the MP packet forwarder for the US band. We could see loraserver getting and accepting the join requests, but at the end device we saw a “denied” status after the join request. We switched back to the poly packet forwarder and everything worked fine again, so our guess with @dhinojosac is that there’s some parameter (which we haven’t found/fixed yet) in the newer packet forwarder that messes the downlink messages and thus the join fails at the node’s side.
I’m not sure what packet forwarder you are running, but if it’s the mp_pkt_fwd, you could try switching to the poly_pkt_fwd to confirm or discard issues with the packet forwarder.
Apart from two RAK831s, ee own a Multitech Conduit gateway too, which uses and older packet forwarder, and it works fine with our custom nodes. We also own an mDot node but haven’t tried it with the mp_pkt_fwd. We could do some tests to check if we encounter the same issue as you.