The garden is surrounded by others, but doubt it was neighbours as the treats were all in one area. We know both next door neighbours fairly well so doubt it would be them and they were at least 6m from the back fence.
We’ve not let him eat any and my wife isn’t keen on testing them!
I know plod won’t do anything, but if there is something suspicious other people might report similar (or not, hence asking)!
He doesn’t bark all day/night and isn’t left on his own much. Edit: we know neighbours pretty well and they all say he’s quiet when we’re not there.