Yellow spots in printed areas

I print on Hahnemule museum etching paper with carbon black ink.
I have yellow spots developing on the paper weeks/months after printing.
these appear on both the front and back of paper in the printed area. any ideas?

The paper has most likely been exposed to some form of either acid or sulfur contamination either within your printing room/studio environment, or previous to being inked.

Exposure of contaminated paper to air and printer ink can make this appear.

Expose the paper to UV light (direct sunlight for a few days) and see if the spots go away. It could very well be malformed optical brighteners that are reacting. They can be cured out by UV.