Hello,

I bought Tp-link Archer AX55 for Network Provider using PPPoE and VLAN Tagging (IPTV).

I configured VPN Server for Wireguard and I have problem with network stability.

At the beginning of file downloads or speedtest, the download speed is high and after a few seconds drops to 0.00 Mbps.

There is no problem with OpenVPN.

Additionally, I bought a second identical router to exclude a problem with specific software and unfortunately the problem occurs there too.
I did an experiment on another connection (regular DHCP instead of PPPoE + VLAN) and Wireguard works correctly.
So my suspicion is a Wireguard error with the PPPoE + VLAN connection (tagging).

I also did an experiment to exclude the problem of my connection - I set up Wireguard Server on my laptop, forwarded the port on the router to my laptop, connected from another device and from a different network and the speed is still stable.

Curl:

Speedtest (beginning)

Speedtest (after few seconds)

MTU on router is 1492 (max allowed value).

MTU on Wireguard client I tried adjust from 500 to 1492 (I wrote script to test CURL with MTU value) and for everywhere there is the same problem...