The only thing there that sounds like a misconfiguration is whatever is dropping ICMP frag needed messages, and that is a misconfiguration no matter what. My p

The only thing there that sounds like a misconfiguration is whatever is dropping ICMP frag needed messages, and that is a misconfiguration no matter what. My point is that no matter what MSS you send, that's never what's at fault for PMTU problems, that's not what MSS is for nor could it possibly do the job in all cases, whereas correct delivery and processing of frag needed/packet too big will always work.