My ultra keyed footage starts in black when I use a transition

[HawxyProxy]

My footage is fairly straight forward - I have a subject in front of a green screen, which I've then applied a mask to, to hide the green screen edges, and also the ultra key effect. What I have is the standard result where nothing is seen but the subject. I want the footage to fade in but when I apply a transition it starts in complete black and then fades to be just fine.

The screen grab attached is taken just after the initial complete black screen at the very beginning of the fade.

I've tried multiple different transitions with every usable result being the same.

[HawxyProxy · Accepted solution]

SOLVED: For others looking for the fix on this head here: https://community.adobe.com/t5/premiere-pro/black-flash-during-transition/td-p/11132177?page=1