If I remember right there was a YT video testing this a couple weeks back. Slideshot has no buff text indicator on bottom left screen, but it does activate the moment ammo gets automatically reloaded into your mag when you slide. The buff (extra range + accuracy) lasts 2 seconds from that moment. If by not activating you mean that it's not even reloading ammo to your mag on slide that's another issue I haven't heard about.