Hello!
I seem to have run into this bug. Basically, I've been able to join this world on a private BDS that I operate, with the game giving me a "Locating server" message forever. In the server log, it shows that I've connected, and when I cancel it shows that I've disconnected.
I've also opened the world folder locally, and have been able to spawn in and move around. I just took a few steps and jumped once or twice, then saved and quit, and loaded the world back into the server – still stuck at "Locating server." I then went back into single player and tried moving my character a few hundred blocks away, saving and quitting, then running the world on the server again. Still stuck (though I'm not sure that the local player is the same as the one used when I'm connected to the server, so that might make sense).
What can I provide that will be of help? I have telemetry and logging enabled on the server, and I have the world folder as well as the entire server. Heck, the server's just hosted on an Azure VM with nothing else on it, so I can even give someone access to that, if it'll help.
Here's a link to my affected world: https://1drv.ms/u/s!ApN0xHnpwrOwgeZU8Lby_gviCDWY9A