Bug/Issue PC - LAN Only - No Invite Code option

I am unable to play with my friends because the only option available to me is for LAN. I purchased and installed the game about two weeks ago and did not opt in to any betas.

A list of things I've tried:
- Reinstalling Stardew Valley
- Verifying Steam Game Cache
- Verifying the game was the most recent version
- Installing Visual C++ Redistributable Packages for Visual Studio 2013
- Reinstalling Steam
- Changing Steam pirvacy settings
- Changing connection from Ethernet to WiFi (including disabling the Ethernet Adapter)
- Allowing Stardew Valley access through my Windows firewall and antivirus
- Forwarding ports
- DMZ'ing router
- Waiting several minutes at the start screen before selecting the Co-op option
- Having a friend invite me through Steam
- Joining a friend through Steam "Join Game"
- Creating a multiplayer world and inviting friends
- Trying to opt-in to the old beta with the "jumpingjunimos" code
- Checked to see if my computer was plugged in (it was)

None of the above suggestions solved the problem. It's entirely possible that I didn't correctly try one of these options, so if something sticks out I'm willing to try it again. Other than that, I'm not sure why I am still not able to play with my friends, since I've read that this issue was fixed in a previous update. The only thing I haven't tried is trying Stardew Valley on a different computer on the same network, mostly because I'm not able to test that.

Any suggestions and help are welcome!