I have an AT&T 4G LTE modem into an ASUS AC-3100 router which is running CyberGhost VPN. When I try to use UDP in the VPN I can ping hosts but cannot browse to any web page. It times out. I've determined it is an mtu problem. When I set mtu on my win 10 computer to 1300 it works ok and when I set it to 1330, it fails, but, of course, I can't set mtu on any of my android or apple devices so I'm stuck. Normal mtu should be 1500 throughout the network.

My question is how do I determine where the problem is? If I run pingplotter with UDP and uncheck the "fragmentation" selection I can quickly see the problem but not where the problem is. It still shows all the hops as completing when I think if a UDP packet is "lost" by a router along the way there is no record or error message given back to the source. Where along the way is the mtu set too low and how do I find it???

Any help would be greatly appreciated.