Graham
Has this problem just started today or have you had it previously. Also how do you know it is your data which is making the aircraft appear on Planeplotter and not someone else?
When it is in your myflight does it have the globe beside it when it is not on the screen?. I ask as on some occasions I have aircraft in my flights with no globe due to the screening effect of the building which cuts off the ADSB part which still allows sufficient signal through to allow the aircraft details to appear in my flights, during this time it doesnt appear on the map. As you can see I am not very technical with this so may have some of the terminology wrong.
Alan