Unresponsive screen, except for when in power saving mode?

UPDATE: Power saving mode is actually very rarely fixing this problem. When I first posted this, power saving mode had turned for the first time while playing it, and it seemed to fix it. Now however power saver doesn't do anything to help it, although sometimes it seems to smooth the app out a little.

TLDR; Screen is very unresponsive, power saver stops it. Why??

I have an HTC M8 and have been having problems with Pokemon Go. The touch screen becomes quite unresponsive and laggy when playing this game. I have to tap/swipe multiple (sometimes ridiculous amounts) times for things to register. This hasn't ever happened before on this phone, and doesn't happen with any other app. As soon as I leave the game, the screen becomes normal again. The phone is normally never laggy or unresponsive. The game however is playable, but it makes the more complicated mechanics of the game impossible (timing your Pokeball throw, and gym battles). I thought this might be something that couldn't be fixed, but I noticed today when power saver mode turned on, that everything suddenly became fine! The screen was very responsive and the game played perfectly, for the first time since I got it. Any clue as to what could be causing this and what I can do to fix it? I have a custom ROM and kernel: CM13.0 nightly, CM kernel.

Thanks in advance.