Sorry but no clues on this error reported.
It seems that any packets are blocked thus the access were denied.
Maybe you can adjust your firewall rules to check which one caused this issue.
Thank you.
I've figured it out. It wasn't any firewall rule but rather an inconspicuous setting I had activated.
It was a setting that gave me an overview of encrypted vs unencrypted traffic. Pretty useless in my eyes as it specified that it wasn't intercepting encrypted traffic or the likes.
Anyway, it seems it still interfered with encryption. Disabling it fixed the issue.