It's working,this morning. PG elves must have snuk in last night and fixed the issue or..... I was so brain dead at that point I couldn't see what I thought I saw.
I have no idea other that changing the key which forced a transpose,knocked a bit loose in the programming, so it would work.
The same 2 bar acid loop from last night, set to retrigger on "Chord" does exactly that, re trigger every chord and if there is not a chord, it plays the second bar of the loop.

Mysteries of the great PG.
Thanks Wyndham