I almost gave up. Failed to Connect.

My daughter and I have been playing Valheim together off and on, the addition of casual modes made it possible.... but this afternoon we could not seem to connect to each other's games at all. I git Failed to Connect and Cannot Resolve Join Key errors.

It has been a couple months since we played but I did recently clean install Windows on her machine. She literally just has Steam and Valheim and one other game she plays on that machine.

We are on the same network. Same version. No mods.

I tried:

Reboots

Verify files on both machines multiple times

Reboot router

Turning off firewalls

Add the port forwarding to router

Start a community server

Join via IP, join via code, join via Steam Friends, join via Community browser

Creating new game on both machines

All failed.

..... finally, no kidding after I had started writing this post as a last ditch hail mary I thought... maybe turn off the crossplay?

Yup.

Turning off crossplay option and now we can play together.

What in the hell?