I will be unable to draw. Another issue I get is the pen and brush and other tools revert to a selection tool. So I can only select and not draw anything.
I have had same issue before. After I checked had selected the correct drawing and correct layer and it still didn’t work, I saved, shut down, and reopened. Worked after that. Can get to be a bit of a pain if it happens often, but has only happened a few times…so far.