Hi there, I've been experiencing this one for some time now but rarely at a time when I have time to write it down.
I use a Korg nanoKontrol2 to control my VMIX session I have assigned a particular fader to control all videos (there are up to 6 in any show) for playback into the show, I also use it to control the level of an NDI input as well via a single fader assigned to the volumes of all channels - as there is only every going to be one playing at a time it saves space on the MIDI controller.

It appears that if there is a video missing file or an NDI source is not connected, moving the MIDI fader that controls all of the input levels results in the MIDI to stop working, only solution is a relaunch of the program, and making sure all sources are present (even if one may not be used in an episode).
Wonder if this could be addressed as often the only time you notice is either when you are live, or just about to be!

Thanks for a great program.