Colorprofile PNG

Yes, that's apparently it then.

I have a couple of PNG actions - including one for screenshot > assign monitor profile > convert - but they all use Save For Web.

Just tested it again: I'm working on mac: If i make a screenshot the colorprofile of the Screenshot is the profile of my monitor (EIZO CG2700S). When i convert now the Profil to my standard rgb profile (ecirgb v2) and save this picture as tif with an action the colorprofile is gone. When i save it manually the profile stays.
Looks like it is a bug with the action-saving step.

Can't replicate here. If the PNG has an embedded profile to start with, it is saved as tiff with that profile still embedded.

However, it's true that embedding profiles in PNG has a long history of various bugs - to the point where I now consistently use Save For Web, which has always done it reliably and correctly. I haven't trusted Save As (or Export) for a long time.

So I don't doubt that you see what you see - but when I test it here now, it works correctly.