Unable to connect to Bedrock Server when online-mode set to true.

Recently (it seems to coincide with the downtime for Realms), people are unable to now connect from multiple devices (Mobile, PC, Switch, PS4) to a dedicated Bedrock Server.  The message displayed is 'You need to authenticate to Microsoft Services'.  We've tried signing out & back in to the Microsoft account on the relevant devices, even as far as completely removing & re-installing the game itself.

If I alter the configuration and set the option online-mode to false, this obviously allows people to then connect, however, this also prevents being able to limit players using a player whitelist (which we have in operation).

I've tried redeploying the bedrock server instance to no avail, it is currently running version 1.16.40.02, and nothing else has changed with the setup either before, or after this issue began.  It also seems to not coincide with any updates to Bedrock on any of the platforms in which the game is installed.

I've also performed a packet capture against the server to see what is coming in & out, and all I can see is the connection to the BDS instance itself, so I'm assuming that whatever the authentication validation step takes place, is entirely client bound?