Cued music being heard in Rec Out when using Crossfader (across all Pioneer Mixers?)

I've been doing some Live Streams I've had to later on delete.

I DJ progressive house music and moved away from using the up faders, preferring the Crossfader with EQs (and all faders left up).

In doing so I have encountered the following issue across several Pioneer Mixers (including a DJM900nxs, a new XDJ-XZ with updated firmwares)

Step by step:

1) A track is playing on channel B, the crossfader is across as far as possible into channel B

2) This is being recorded using the USB interface into a Macbook Pro 2015 (Mojave), with OBS software to live stream picking up the input as the DJM900nxs (or whatever Pioneer hardware is plugged in)

3) I play a cue'd track which should only be heard in my headphones - it does not come out of the Master speakers, but the Rec Out picks it up quietly as if the cross fader was maybe 15% across into A when it is right at the edge against B the whole time.

4) I am leaving the up Faders "up"

5) FX channel: Master

6) At some stage in this process I am moving the headphone setting from CUE to Mixing / Master. I am unsure if this is affecting it?

My goal  is to be able have the audience who are tuned into my Rec Out (USB) to only hear the same music as the Main output and to get rid of this "leaking cue".