Q: iBooks is going dark

Hello,

I have been a user of iBooks for a long time, but since the upgrade to iOS 9 my iBooks app has been going dark when zooming in on a page or trying to change between pages. This is annoying because I use the app for PDFs at school and when I need to go back or zoom in, the screen turns black and I have to get out of the PDF and get back into it again. Why is this happening? Does anyone have the same problem? As you can see in the image, that's what's happening and it is not pleasent.

Thank you for your help.

Sincerely.