I answered your question on another forum. But just to answer it here as well in case someone doesn’t see the other one:
I just tried it. The workaround works great. There is a bug in the Screen Key. Perhaps I didn’t explain it fully. The motion has to be in the sequence with the explosion. Try this:
Create a new sequence named “Explosion”.
Add the shot to track one of the new sequence.
Add the Space Explosion clip to track two.
Temporarily add a Luma Key to the explosion…this is only temporary.
Add the motion to the Space Explosion clip in track two.
Apply any necessary keyframes to control the motion.
Once you are happy with the results, delete the Luma key, then delete the clip of the shot, and move the explosion to track one (optional)
Now put the Explosion Sequence into the Master Sequence over the original clip of the shot. Apply the Screen key.
That ought to do it for you since it does it for me.
Of course, with your explosions, you might just say to heck with it and use a Luma Key instead of a Screen Key. But the workaround doesn’t take that long. You decide.
Steven
https://www.stevengotz.com