Scopes and optics are a commonly overlooked culprit when experiencing accuracy issues with a gun. Mechanical failure like a detached or broken reticle will point randomly at the target after each shot jostles the part around in the tube. Same with a scope of lesser quality incapable of holding its zero. Loose screws on the scope or optic mount will change the point of aim after each shot. Same for a red dot on a slide: if it is loosely attached, it will not point twice at the same point. After a few shots, it can also shear off the screws and fly off the gun and possibly break upon landing (or injure anybody in its trajectory).
Some attachments may be secured improperly and move during the firing sequence, throwing the gun off axis before the bullet exits the barrel or changing the guns behavior every shot. Check and secure everything as needed. Some improperly mounted accessories can also touch the barrel. A loose or flexible handguard can touch the barrel when the rifle is resting on the forend, but otherwise look fine when off the rest. Take time to look for any issue that is not evident other than in firing position.
A muzzle device that is not securely attached to the muzzle will create random barrel harmonics and ruin accuracy. This can create a dangerous situation as well: a bullet may strike the device and fly off course, but it could also fragment and possibly inflict injury to the shooter and/or bystanders. Make sure you regularly check any muzzle attachment, and having the proper tightening tool in your range bag or vehicle can save you a trip home.
Sling attachments are a sneaky source of accuracy issues. Sometimes, the bolt goes through the forend of a rifle and touches the normally free-floated barrel. This will usually happen in flimsy synthetic or flexible wooden stocks that bend upward when rested for shooting. Filing the offending protuberance will address that.
Finally, some accessories may simply not jive with your gun or shooting style. I have had bipods push the gun up during recoil, sending the bullet up a variable amount each time. Same with shooting sticks which are notorious offenders for such felonies (these are useful tools and there is a proper way to use them). If you have a newly attached accessory and experience degraded accuracy, take it off and see if this solves the problem. The accessory may have to find another gun to hang out with (or from).
Accessories are great when they serve a purpose and enhance the gun’s function. I believe less is more in the case of accessories, and that they should be carefully considered, no matter how cool they look or are.