Problem exporting green screen video with Ultra Key effect

[Isaak5C92]

Hi, I'm working on a video with a lot of green screen segments. I'm using the Ultra Key effect, and in Premiere's program monitor the results look fine:

But once I export, the resulting file shows a completely unrecognizable result:

At first I though I might be missing some important detail in the export settings, but after some tests I can confirm that the exact same problem occurss both when exporting an h.264 and a ProRes 422 - so probably there is something else going on.

The effects look like this:

Nothing out of the ordinary in the sequence:

My MacBook:

Could it simply be a processing power problem? Or can anyone think of other troubleshooting measure I could take?

Thank you!

[Peru Bob]

If you bring the exported file back into Premiere Pro, does it look OK?
How are you viewing the exported file?

[Ann Bens]

MIght not be such a good idea to add lumetri and ultra key at the same time (or wrong stacking order)

I would do ultra key, nest then add Lumetri