So, the oil cap has 3 prongs/legs. Depending on how well the plastic panel to which the cap is attached was installed, the little metal insert attached to the plastic panel with 2 small bolts might not lie straight. If there is a little bend to that metal insert, say one of the bolts is over-tightened or some warp in the plastic, one of the cap's prongs might fail to catch the metal insert.
This means, when installing the cap, it is imperative to check that all the prongs are inserted. Wiggle the cap to see if there is any play. Even a little play might be a sign due to the failure to engage well.
I am appalled how poorly the caps are done on this expensive bike. Don't get me started on the radiator cap, or I can blow a cap of my own.