I just noticed some artifacts in one of my images:

I just did a quick edit, to bring out the problem more. That's the stacked image of 20x300s subs, but it's in every sub.
It looks like Amp Glow to me, but I have the ASI533MM Pro, which should have none.
But what is it then? Dirt, smudge, whatever on some part of the imaging train? Light leak?
I took another image after that, and it didn't have this problem, but those were just 60s subs, so maybe I have to try some longer darks, to see if it's coming from the camera itself.