Constant screen flashing black and occasional crash

For the past 3 months at least once every game my game freezes and the screen turns black for a few seconds, sometimes showing a screenshot of me from before in the game (i.e. my champ standing at shop a few levels lower than right before it happened.) Went through Riot support a couple months ago and they had me do a few things and nothing fixed it and after emailing a few times I gave up.

I initially thought it was my computer overheating and freaking out, but after cleaning my computer then booting up other, more graphics intensive, games they all worked fine. But league was still giving these black screens.

Is anyone else having this problem? Or have any possible advice?