Sound from all Playback tracks drops out

I have a Concert currently containing 5 patches/songs comprised solely of Playback tracks with backing track sounds on them. This had been working for quite a while, then suddenly a few days ago, the last few seconds of playback of every song drops out! So, the band and I jam with any of those songs from start to finish and then several seconds before the end of the song ALL of the Playback tracks quit playing audio, even though Mainstage is still processing the patch (it plays the patch until the very end as it should but you can not hear the backing tracks).

Something to note; this only happens when you play those patches start-to-finish. If I skip several markers (ie, "Go to next marker") at any point during play then it will continue to play all audio to the very end, as it should, and you can hear all of the Playback tracks.

I've messed around with several settings and even took an older backup copy from a month or two ago and used that, but the problem persists.

Thanks for your help. We've spent hours trying to diagnose this problem.

Macbook Pro

High Siera 10.3.3

16 GB 1600 MHz DDR3

CPU usage around 3.5% - 4.0% for Mainstage

(Have users by having issues related to recent Meltdown and Spectre patches?)