UPDATE:
So I’ve started a fresh project with 4 new PUM’s and have had a bit more success in the way of consistency of keeping loops alive 
I am noticing that there seems to be some filter settings per track that REALLY effect the behaviour of PUM’s. The Width, Base & Q?
Also, after building up some loops, when I then move back to a previous track - there is a huge BOOM of feedback that scared the bejesus out of my one year old (poor thing)… Any suggestions to what that could be and how it is “obviously” related to my previous issue in the post above?
Are the mixer DIR and record settings GAIN at play here?
I hope this is also helping others as I troubleshoot this.
I really…really…want Pick Up Machines to be solid enough for reliable performance.
Thanks!