sensitivity keeps changing in game

Corsair M65 mouse, same issue for me.  Hasn't happened in CS:GO or Overwatch for me but perhaps it is the mouse.  Not sure yet.  My DPI is set to 400, and twice now while in a fight the DPI changes to what feels like approximately 100 for 10 seconds or so until I die.  No input lag, but the mouse just moves roughly a quarter of the distance it previously did.  I have never reproduced it in training mode, and it's hard to reproduce, but it's there and it ruins games.  I'll be purchasing a different mouse to test further, and I'll follow up. 

Edit: in my case, embarrasingly enough, I believe it was because I didn't realize that arc stars "stun" you which reduces aim sensitivity for the duration of the stun.  I'm guessing that was the reason.  Figured it out as soon as it happened with another mouse.  Lol.  Although it would be interesting to see if anyone could effectively use the quick DPI mouse settings to basically undo the stun right away and then switch back to original DPI after it ends.