Hello! As for the problem, I do not know the cause of the problem aside from the possibility that "X-plore" could be the problem. This is not a problem I usually encounter. I use an app called ReadEra, which is free (there is a premium version that I use which has more functions), and I never had any problems. The app also has a volume button to flip a page, a brightness adjustment bar and many other features.
So try using ReadEra and see if it works.