[Bug]: Auto MTU seems not to work

[theklausklausen]

Describe the bug

Not sure if a bug but anyway.
I set up a fresh instance (v15.1.0) with default the Android client MTU is set to auto (placeholder text). I can connect to the server, i get Latest Handshakes, i can ping hosts in my home nework and i can curl HTTP traffic. I cannot curl HTTPS traffic, the response is unexpected eof while reading.
If, however, set the MTU on the client manually to 1150, it works perfectly. Since i'm not sure whether this is acutally a good idea and this does not scale, to do that manually on each client, i don't want to do that.
Server side i cannot set the MTU below 1280. ChatGPT recommended following hook: iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu but apperently this is not supported.
On v14 this worked out of the box without any MTU configurations.
If this matters: running in Kubernetes with Cilium cni in native routing mode, wireguard port bound to loadbalancerip populated via Metallb IP. If any more info is needed, let me know.

Expected behavior

Work just fine!

Relevant log output

[kaaax0815]

if you download the config from wg-easy the MTU field should already be filled.
wireguards auto mtu is not the best, and sensible default work better in most cases

[theklausklausen]

Yes i got that. But for some reason the connections work properly (including ssh/https traffic) only, when I set the MTU to 1150. WG-Easy does not allow values below 1280. And as mentioned, in v14 this was not a problem, even though I cannot remember configuring MTU at all.

[kaaax0815]

What is your connection that you require such low mtu?
mtu is limited to 1280 as ipv6 requires that

[theklausklausen]

It is an IPv4 connection. Not sure what answer you expect (sorry). If I can help with information, please let me know.

[kaaax0815]

i meant more like cellular, special nat-ting, stuff like that. because i've never seen mtu under 1280

[theklausklausen]

On phone side simply cellular. In Server side it is single Nat, wan is on a vlan, gpon (ftth), running in a kubernetes cluster (doubt that matters).