Hi,
I bought Artstudio pro for mac today, I was trying it out with my Huion drawing tablet when I faced this issue. When I change the brush size using the pen and try to draw, the brush size changes to a bigger size automatically and I can't draw anymore. If I change brush size using mouse and then use pen to draw, it works fine. It tried to look if there is any setting I have to change but nope, settings are very minimum and could not find any settings to fix this issue. To change the brush size now I need to use the mouse and then draw using pen.
It may be that I am new to this app and missed some setting that I have to change to work with the drawing tablet.
I am attaching a video of what is happening.