Ink fixative

Bump.

no help with fixative I'm afraid

did you get the correct acetate? You probably did, but it's just a thought. I've done prints on acetate and never had that problem. The acetate I used had a side that felt slightly gritty and held the ink well.

You could try building up very very thin coats of varnish and see if that works - spraying so as not to touch the surface. Experiment first on something that doesn't matter.