In recent releases of UltraVNC, there have been a few “growing pains” that needed to be worked out.
The 10.25 release should alleviate these pains and allow you to resume pushing out UltraVNC with Microsoft Windows Authentication (MsAuth) again.
Once you’ve upgraded to the latest release, you can simply re-deploy your existing UltraVNC profile to an affected machine and the problem will go away.
Thank you to everyone who helped us pinpoint the source!