Could be your stock to low.
I'm gonna go with Chippy on this one.
You have just changed from shooting with your right eye, to both eyes and you are right handed.
Your ABT scores have improved but you are now missing R/L birds.
This suggests that you were missing more targets that were not R/L, when your left eye was shut as you could not see them as well as you can now.
I would say, that it is possible your comb is too low and your right eye is partially obscured by the back of the action. Previously, with just one eye there is no dominance issue, There is only one choice for your brain, regardless of how obscured that view might be.
You will see R/L birds quite nicely, when shooting with just the right eye, pick them up and off you go, but targets on the other side of the gun are less visible.
What is probably happening, is on some targets your left eye IS taking over, because your right eye is obscured and your brain now has a choice of "Cameras". So while you are not applying lead (from what I understand of Trap, you just shoot it), you are shooting in front of the R/L targets, because your left eye is shooting them.
Sporting is sporting...are you shooting gun down?
Anyway, the simple fact is; you have changed one thing - the number of eyes involved. So probably stance etc, though valid, is not the issue.
Easy enough to try. Raise your comb up by 3-6mm with a suitable material (card and tape).