Lost connection to server at 'handshake: reading initial communication packet', system error: 0

I'm currently somewhat lost too! I had to restore my nextcloud installation from a backup. Since then I get the above error and I don't know what the reason is. I have already tried everything in the connection chapter without success. For mysql I have opened port 3306 and set bind-listener to 0.0.0.0. That should make it work. If I call the mysql client directly, I can log in. I suspect it has something to do with the SSH tunnel. I can call the plink successfully manually. Does anyone have any other ideas as to what the problem could be? It used to work so far and I have no idea what might be the difference now. Probably a small setting somewhere... Thanks in advance.

I found the reason: AllowTcpForwarding has to be set to yes.

I have undone the changes mentioned above.