Liveid unable to connect to a specific world in multiplayer

I'm hosting a minecraft bedrock dedicated server running in Azure, and have lots of folks connecting to it.  It's been working great until a few days ago when suddenly a single user can no longer connect to the world.  Every other user can connect to the world just fine except this user.  The specific failure mode is that the user gets stuck on the "generating world: locating server" screen.  Other users inside the world see the user connect, and their body loads, but is not interactive.  Leaving for 10 or 20 minutes at the loading screen doesn't help, and eventually the user gets disconnected.  

I tried the following steps to debug: 

• uninstall and reinstall minecraft: doesn't help

• Connect from a different machine: doesn't help

• Connect from a different platform: doesn't help (I've tried windows 10, android 10, and xbox one, all with the same effect)

• Connect from a different network (i.e. a friend's house): doesn't help

• Load the world onto my local PC and have the user connect to it: this also fails

• Create a new world on my local PC and have the user connect to it: this succeeds!  but doesn't help 😞  

• Load the world locally on the user's PC and have them connect to it: this succeeds!  But doesn't help 😞  

• clone the world on my local PC, and have the user connect to it: this also fails

• Have the user logon to the world from a different xbox live account: this succeeds, but again, all of the items in their inventory and nether chest are now lost, so it helps, but doesn't fix the problem

• change map specific settings (chunk size, fire spreads, etc.) and have the user connect: doesn't help

I'm open to ideas on other steps to debug.  I tried to find server or client logs, but the minecraft server logs are pretty unhelpful, and there doesn't seem to be any client logs.  

I search for similar bugs on the minecraft bugs list and forums, and the closest bug seems to be related to logging out of the world while in the nether or entering or exiting nether portals at certain coordinates.  The user was not currently in the nether (their body spawns in the overworld when they hang), so that doesn't seem related.  

Client behavior: The client behavior is interesting.  When it hangs on the loading screen, it is still "cycling" the status indicator, but pressing cancel doesn't do anything.  This itself seems like a bug.  If i terminate the world while the user client is hung, it will disconnect on the client side and the client will once again become responsive.  

If you have any other ideas, or need other repro steps, please let me know.