Can't play multiplayer past tutorial, consistent network error (E015-7)

[Rainity]

My family and I just bought the game to play together online, but we can't play the campaign past the very first cooking session (the tutorial). All of us have freshly started the game (and bought it specifically to play multiplayer).

We..
- are all playing via PC, via Steam
- are all located in Germany (Steam download region: Germany - Dusseldorf)
- are not using a VPN
- have freshly installed the game
- have NAT open

We've tried ...
- the Overcooked! campaign and the Overcooked! 2 campaign
- only having two of us, who are playing from the same network, join a session
- having different session hosts
- playing the tutorial level in singleplayer and trying to start multiplayer after that
- verifying game files
- following the network troubleshooting guide from https://team17.helpshift.com/hc/en/3-team17/faq/97-troubleshooting-network-connectivity/

I'd like to mention that we play other games together via Steam and never have issues, so it's not a general network, firewall or Steam issue. We've spent close to 2 hours in-game trying to troubleshoot this already.

[Team17_CS]

Hey there Rainity,

Thank you for contacting us! I´m really sorry to hear that you and your family are unable to play together. I understand how annoying this is but don´t worry, let's fix this issue!

We will need to review your DxDiag file and also the ones on the other PC's, so if you could send us this information from each PC, it would helps us a lot!

1. Hold down the Windows Key and press R.
   
2. In the Run dialogue that appears, type dxdiag and click OK.
   
3. Once the DirectX Diagnostic Tool opens, click on "Save All Information."
   
4. Set the file type to Text File (*.txt).
   
5. Save the file as DxDiag.txt on your Desktop for easy access.
   
6. Finally, please attach the DxDiag.txt file in your reply to this email.

Keep us updated!

Regards,
Team17 Support

[Rainity]

Thanks for your quick reply, I've started a support request via the Team17 website contact to be able to attach the requested files.

[Rainity]

Here's the reply I received, in case anyone else is stuck as well.

"We have received similar reports from other players on this issue, so thank you for sharing your report with us we greatly appreciate it.

We have now passed this over to the team to investigate further.

We're unable to give any timeframe on how long this may take to resolve, however, we hope for a fix as soon as possible.
Our apologies for any inconvenience this may cause in the meantime.

Thank you for your patience in this matter"

[Dicewolf]

Originally posted by Rainity:

Here's the reply I received, in case anyone else is stuck as well.

"We have received similar reports from other players on this issue, so thank you for sharing your report with us we greatly appreciate it.

We have now passed this over to the team to investigate further.

We're unable to give any timeframe on how long this may take to resolve, however, we hope for a fix as soon as possible.
Our apologies for any inconvenience this may cause in the meantime.

Thank you for your patience in this matter"

Gonna be honest with you, this bug has been in this game since launch, almost 5 years, and they say the same "Were working on it"... no... they really aren't.