UDP doesn't support PMTUD so turning on "Adjust TCP MSS" won't help in your situation, you can check the MTU settings on your PA device by using the command - "show routing fib" and to check if jumbo frames are enabled - "show system setting jumbo-frame" if your device supports it. A simple way to find the max MTU between two nodes is using the ping command (on Windows box) using the -f and -l options, start by doing a ping from device A to device B using - ping -f <device B ip> -l 1472 (28bytes overhead) . If the MTU along the whole path is 1500 you should receive a "reply from <device B ip> " message but if the MTU is lower you get the "Packets need to be fragmented but DF set" message. If you get the latter message keep dropping the -l option on the ping command by 10 or 20 bytes till you get a "reply from <device B ip>" message and that + 28 bytes is your max MTU. If the 2 devices are on different networks then it will more than likely pass through a router or firewall that blocks ICMP traffic and won't respond to a ping. In this case you can still use the same method only that when the packet size is within the MTU you'll just get a "request timed out message" but still should get the "Packets need to be fragmented but DF set" when the packet is to large.
... View more