About a year ago I made a piece of art for a poster background using the watercolor tool when working on a mask. I tried to do the same technique today but found I couldn't replicate because I was restricted to the pixel brushes. When I opened the original poster file on Illustrator for iPad the mask layer is no longer a mask, but a pixel layer. Has there been a change to the code or anything like that preventing watercolor/vector brushes from being used to hide/reveal on mask layers? If so can we put the feature back? I am unable to recreate the same effect for my work and am highly disappointed.
There has very likely been many changes to many features in the past year. I'd suggest going to the Feature Request page (App settings > Help > Request a feature) and ask if they can recreate the ability to do what you used to be able to.