Thanks for trying, it is appreciated. I don’t think that this IS the culprit, but was only one of two new things that I was trying, hence the OP.
It is rare that I fly flightplans as I feel that they are not well implemented at present within the sim, but just wanted to try a few things out and this would have been my second suspect( I normally input directly from Flightplan database or similar and monitor via Little Navmap on a spare laptop)
As I said in OP, I normally have a good experience with stability, which is what made me price up my ears a bit. Thanks once again.