I can start up my project just fine and make a save or two, then I notice that changes are no longer loading, so I check the GMLive console and that's being spit out instead. It also includes my IP address (the router's) as well as what I assume are port numbers starting from about 65,500, ticking up every time the message is output, like it's trying different ports or something. If I stop the game preview and reload the project, it does seem to usually work again briefly. It was working just fine the last few days so it's possible that when setting up a new router, I accidentally set something wrong.
I know the help file says to make sure that no other applications are using the same port--the only other applications I have open are Firefox, Chrome, Steam, and Discord.