Server stops and disconnects all players every time a particular person try's to join server

[cameron fogg 0]

I'm stumped, I have a server hosted through this site that works completely fine when I'm playing alone, but as soon as my friend try's to join the server it stops and disconnects both of us.

[Blisto 4]

I haven't experienced the issue myself but maybe some of these methods can help https://frondtech.com/valheim-server-crashes-when-friend-joins-how-to-fix/

Edit: Reading further there might be some programs running on client machines that can crash a server when they join it.
He isn't running ASUS ROG Gamefirst on his computer by chance? It's also the one listed in the post above