Small problems

I really love this app but I have a problem. It may be my device, but once Im almost finished my art, when theres lots of layers and I zoom in and out, a blank square appears on the canvas that I have to go over and fix. Also, sometimes I zoom in, and when I zoom out it crops the canvas to that size. All in all this app is wonderful its just the small problems

Violinist9803 about MediBang Paint for iPhone, v8.2