Bug/Issue Connection Failed

I've been playing with 2 friends of mine for two weeks and we never had problems to connect, but me and my sister always face "Connection Failed" after seeing "Connecting..." for a long time when we try to play together. I thought it could've been only me having SMAPI but I deleted my game's folder and reinstalled it and the problem persists.

The host always loads the savegame with enough cabins going in Co-op > Host. We have tried joining by:

• Clicking on Joining game on Steam chat
  
  
• Accepting the game invite on Steam chat
  
  
• Typing in the savegame invite code
  
  
• Clicking on each other's savegame in the Co-op main menu And also:
  
  
• Deleting our games' folders and reinstalling on both PCs
  
  
• Disabling Windows Security antivirus and Windows Defender firewall in both PCs
  
  
• Restarting Steam on both PCs
  
  
• Restarting my modem
  
  
• Port-forwarding my modem as instructed here: https://www.stardewvalley.net/multiplayer-troubleshooting-guide/
  

In the first 3 times, the problem was solved by restarting Steam, but in the fourth time nothing worked. The only things left to try I can think of are: port-forwarding and restarting her modem, and installing the game in a different laptop of hers.

Any other fixes? It's sad because we were really enjoying to play this game together, and now it seems impossible.

 

For what is worth, I have tried, again, a bunch of other possible fixes I had found on the Internet, and although those haven't worked, disabling all the firewalls on my modem settings page fixed the issue.

 

Did you come up with a solution? I tried everything