Connection to wireguard VPS issue

[crt333]

I'm running OPNsense 25.1.8_1-amd64 on a n5105 box, it's been working for years with various VPN providers, like Torguard, Proton, (all wireguard) etc.

I purchased a VPS, installed Debian and Wireguard on it.
- connecting from my Pixel 7 phone directly to the wireguard VPS works fine
- connecting my OPNsense router to the wireguard VPS results in varying problems:
  - gateway monitor looks fine, ping and traceroute seem to work
  - loading web pages on clients is mostly broken (clients connected through OPNsense to VPS):
    - from Pixel 7, a few web pages load, most don't
    - from Linux mint a few web pages load, most don't
    - from Windows 11 most web pages load (odd)

Seems like it might be a MTU issue, but I don't see any ICMP firewall issues that might be messing it up, especially since Windows 11 seems to work?

I'm stumped.