Sometimes there are fitting issues between our short-throw safety selector and the Geissele trigger. Please take it to a qualified gunsmith. Like all aftermarket products that deviate from "Mil-Spec", some requires a bit of fitting and some are simply not compatible.  The key element is that the short-throw safety works with a "Mil-Spec" AR-15 trigger.  If it does, there is nothing wrong with the safety selector.  With that said, due to various aftermarket trigger designs, sometimes issues arise.

The top deck of the Geissele cast trigger bar that engages the safety cylinder is unusually shaped and thick compare to standard trigger.  The standard Mil-Spec trigger bar is thinner and has parallel surfaces.  The top surface is usually machined for tolerance. If you look at the Geissele you will see the top deck starts at extremely thick and then tapers down to the tip of the trigger bar.  This is the design difference that causes compatibility issues.  

Furthermore, the top deck surface is not finish machined and left as cast.  We have tested our Short-Throw Safety against various Geissele Triggers before the launch years back and without issues, at least with the ones we had.  However, casting tolerances varies greatly, with a swing of 0.015" typically.  If that surface isn't finish machined, there will be fitting issues from time to time.  We cannot modify our safety any further for risk of "safety" issues with "Mil-Spec" and other aftermarket triggers.  Our safety selector cores/centers are precision CNC machined on all surfaces in fully automated SWISS machines with a tolerance of 0.0004" or better.  

We recommend slowly removing the material off of the trigger bar top deck (see Image above that shows "deck height") about .001" at a time on a flat India Stone (or equivalent) and test fit the trigger to safety until you get the right fit and the safety freely rotates in FIRE and SAFE.  Keep the surface flat and parallel.  Note that modifying your trigger may or may not void your trigger warranty.