Faded Tools???? Please fix

I have this app on my IPhone 4s and I absolutely adore it, and I dont even have the pro features. But I recently downloaded it on my IPhone 6s and the pencil tool is faded. You have to go over the same spot several times to get the opacity you want. Which is very aggravating because it can mess up your lines and makes odd bumps. I already adjusted the tool to its darkest setting and Im still having this problem. The ball point pen has the same issue. One my old phone I didnt have this problem and I was hoping it could be fixed!
Thank you for your time!

Faded Pencil Problem about Sketchbook®