I work as a range officer at a large county owned firing range.
The two things that I see continually with AR failures are:
1, Under lubrication / no lubrication.
2. Steel cased ammo.
About equal failures from each cause. Not unusually I see both together.
Some shooters are amazed what a few drops of oil will do to improve the
function of their rifle.
Trigger control + Breath control + Sight alignment = Gun Control.
NRA Smallbore Prone Master