Object detection in fast ai

I am hoping somebody can help me because I am banging by head against a brick wall :stuck_out_tongue:
I am using the RetinaNet notebook (link posted in my post above), after running different experiments my results were getting worse and no where near what I got the first time round so I decided to do a check.
I looked at the model where I got good reults, an mAP of 0.36
So I took tha same model, same notebook, same data, changed NOTHING and my results are terrible mAP 0.15. Has anyone come across this before ? I haven’t changed a thing but I know that something must be different and I can’t seem to find out what it is!.
Thanks