Aux Sends being muted when Aux return track is soloed

[MunkeyStu]

So back to the aux send and return muting/soloing issue.
Two tracks. (see vids on FB Waveform group)
https://www.facebook.com/604522153/vide ... 156032154/

1st is working, where I aux send the drums to a separate track which has reverb so I can create a reverb “room”. If I solo the reverb track I can hear just the reverb, because the aux sends are pre volume/pan.

2nd example track is not working.
Exactly the same set-up but when I solo the reverb track it mutes every other track, even though the aux sends are before the volume/pan like the first example.

What’s different between them?
Why does it work on one project but not the other?
Both projects are open at the same time so are subject to the same overall settings.

This is really affecting the workflow.