Mike,? excellent observation.
I will try this scenario on my Pi with bookworm, and replace the /usr/local/bin/rmsgw with a shell script that writes to a log file.
Disconnect the vhf radio, disable the rmsgw_aci, and only have the kissattach, ax25d, and beacon process running.
And regularly check netstat for weird device entries.? This would help verify your theory that rmsgw running on current kernels is a main problem.?
Since moving down to buster, it's been crash-free for me.? Two weeks plus.
Something to try (in all your free time)? let the system run nicely without rmsgw, then turn it on for a bit and if you catch the netstat output with an empty or null value, stop/start ax25d.? Does it become stable again?
