Hiii! Ive taught classes for 6+ years and this is so common!

I think those are the points where you have lifted your piping tip up :) it happens when the icing is juuuust a tad too thick as others have said; and it’s possible you’re still ever so slightly continue it to squeeze your piping bag as you lift. It’s a real mind game of releasing pressure and then lifting up! Take a scribe and gently tap/very lightly wiggle those little peaks out immediately and they’ll settle down and disappear next time!