Thank you for your question. You pictures are not detailed enough for me to make a good diagnosis. So, below are links that provide details about the symptoms of various pine diseases. I recommend you look closely at the Mugo pine and try to match the symptoms with the a listed disease. If you are unable to do this, you might wish to take a sample to the Master Gardener Help Desk (https://elpaso.extension.colostate.edu/landscape-garden-help-desk/) and ask for assistance. There is a microscope at the Help Desk that is used when making diagnoses.

https://www.mortonarb.org/trees-plants/tree-and-plant-advice/help-diseases/pine-diseases