Opensky server resets TCP connection

I have a FlightAware FlightFeeder that is probably running dump1090-fa. I forwarded incoming 30005/TCP traffic to the FlightFeeder.
Opensky's server (194.209.200.101) connects to port 30005 and I can see the planes on my Opensky dashboard. The connection is very stable, there are no dropped packets, retransmissions. However after 2-3 minutes Opensky's server sends a TCP RST and usually waits 1-2 minutes before it reconnects.
I tested the feed with pyModeS and I could keep the connection open as long as I wanted.

Is there a log that would tell me the reason of the disconnect?
Does Opensky use any server other than 194.209.200.101?

I think I see the same problem. I forward the data from dump1090 port 30005 to a VPS because I am on a IPv6 connection, but tried several methods to forward the port, i.e. via a SSH tunnel and a Wireguard VPN, either trough iptables NATing or forwarding with nc/socat. I also tried different dump1090 versions/forks.

With every method I see the connection dropping and reconnecting a while later, but couldn't find the issue.