I've run into a lot of problems with uneven wet washes, splotchy absorption or white speckled dots where watercolor paint will not sink into the surface coating (sizing) of the paper. It appears that Arches cold press cotton watercolor paper has been having an increased rate of sizing failure in 2020-2021. It is possible that during the pandemic supply shortages something changed with their core ingredients to make this paper more susceptible to this issue.
I talk more about my favorite watercolor papers, waterproof pens and inks, paint brushes and more on this page:
Watercolor supplies - list of waterproof ink, pens, paint brushes, paper (both cellulose and cotton, affordable student to pro quality options), swatch card creation and storage, lighting, basics of top-down video making for artists and crafters including camera holders, free and low cost editing software and other tools!