Thanks to all for the input and ideas to check through, the setting i was thinking of was of course "stop at project end" (forgot it was under track view>options) which was set once and forgot a long time ago.
So, knowing that wasnt it, diving through the offending/irritating projects i had sporadic muted/hidden tracks with unused takes & clips moved minutes downstream, and a couple of volume nodes in right field.
I think the lesson to me here is to be more organised with unused material....
By habit i would simply mute, move out of the way and or hide.. so I need to either use a track folder for these bits and not move them stage right, or probably better, store them in the project folder and keep them off the track view altogether