IPv6 tcp connections to the router establish but then time out


I have found out that for some reason IPv6 services on my Omnia router do not work as expected.
The connection establishes well, but then it looks like something is holding the packets.
It reproduces when I try to connect from LAN to a router service. LAN to WAN is fine, and router to router is also fine. I’m unable to properly test WAN to router but guess there would be an issue too.
For example, I have a nginx server, which is configured for keepalive_timeout 65. when I try to load a page over IPv4, it loads instantly. But when I try to load it over IPv6, it loads after 65 seconds. I cannot explain this.
Another example is ssh. I tried to telnet to 22 port over both IPv4 and IPv6. When I telnet over IPv4, it prints me a server version string, “SSH-2.0-OpenSSH_7.6”. However when I try the same over IPv6, it first waits for 2 minutes, then sends the server version string and closes the connection simultaneously.

I have no idea what could cause such behavior…

Best regards,
Denis Shulyaka

This might be related to enabling an openvpn server using foris interface, because I configured that not that far ago.

Well, I’ve just found out that it were my own custom rules for transparent proxing to blame. Sorry for your time.