We tried vMix for the first time last weekend with a stream of Drag Racing from Adelaide Raceway in South Australia. Everything went pretty smoothly except the audio.
We had the commentators feed in as an input but it was almost a full 3 seconds ahead of the vision.
We set a delay in the settings and it all seemed to work fine, except, every now and again, about 7-10 times the audio input would just fail.
The only way to get it back was create a new input, select the USB mixer as input and select.
Within a matter of 5-10 minutes it would fail again.
Sometimes it lasted over an hour but would the fail again.
One "theory" was that it may have been caused by the close proximity of a mobile phone, but I'm more inclined to think it had something to do with the delay as it stopped happening when the delay was switched off.
BTW the stream is archived here:

Yes streaming from security cameras, unfortunately there's no audio input into them so plugging them into the stream doesn't seem an option. We would love SDI etc... But this is an ultra low budget production and the budget won't run to anything like that.
Might delaying the audio via another computer running VLC solve the problem?

Not sure but I will look into it. Certainly not in the mixer supplied by the venue but perhaps we have something available. As I said it's a very low budget shoot so we don't want to start adding too much.