Welcome aboard. So after decocking the pistol you are having some issues. Lets dig into this a little:
1. After decocking - can you pull the trigger all the way back until the hammer drops?
2. Can you rack the slide?
3. Are your problems with firing the pistol after decocking or having other issues like. Magazine not staying seated, reassembling after cleaning, Decocker not acting correctly? We will need more info to help you diagnose the issue.
Decocker is not tied to sights That I know of...Aiming is a user issue NOW that we dismissed that myth of decocker throwing off aim lets get to Firing trigger not cycling, striker not striking? what is the exactlies of the issue are you by chance Leaving safety in the ON position? Photo might aide our corrections. I can make a plethora of GUESSES some are user error which is common I have made same mistakes then Mechanical IE Trigger should not be manipulated while decocking or setting safety BOTH mechanical and User 99% User Error 1% because the mechanical failure decocker/safeties/Trigger bar/springs are NOT designed with those stresses in mind. So more information could help us wade through and get you back on track
Is it the first shot after the decocker? If it is, you are sort of in a double action mode for that first shot. You are using the trigger to recock the striker and unless you've practiced double action shooting, you will have a problem with the first shot.