Remote App - impossible to increase volume again

I downloaded Remote app for my iPhone 6 to be able to remotely control playback on my MacBook Pro during certain therapy sessions. I would often like to fade out the music by slowly decreasing the volume to zero. It is Ok and the volume dot reaches the zero position on the very left. But then the problem starts - it is almost impossible to increase the volume again, while trying to move the volume control to the right. When doing this, the volume control keeps on zero position all the time but the whole page starts scrolling. Maybe after 20 attempts it suddenly moves, but this is VERY frustrating and badly made. I don't know how to solve this crazy problem