I wanted to resurrect this thread because I just found something NEW that works GREAT! I have the MX-3000 software running on 3 different PCs, two running Win 10 and one Win 11. Eventually none of them could communicate with any my 11 MX-3000s (one for each room) via Windows Mobile Device Center, no matter how many times I did the routine above. Then I found a new fix on this site:

[Link: junipersys.com]

and it worked on both Win 10 and Win 11! Download and install the two fixes in the middle of the page and reboot and I am back in business, what a relief!

I should add that I had to redo the installation of the Microsoft USB Sync driver AFTER I applied the Juniper patches on at least one of the PCs, but it worked immediately after that, no second reboot needed.