Server Not Responding When Friend Enters Caves

I'm the host of the game and am running both Forest and Cave servers on a password protected online server.
Friend is playing in the same room, hard wired through the same router. When she tries to enter the caves, the
server gives a "Server not responding" error and doesn't let her connect which then boots her to the game title screen.
I can enter the caves in and out just fine.

Tried so far:

Firewalls both off / game is whitelisted.
Clean reinstalls of both games.

Searching through year old forum posts didn't seem to narrow down where we should start for troubleshooting.

Also there are no MDMP files in our DST > bin folders so I couldn't link those.