I keep an inventory of alg trigger - ALG Defense ACT Advanced Combat Trigger for AR-15/AR-10

AR-15 triggers have a limited life. Life expectancy is 5,000 rounds for reliability. I usually stretch them out to 10,000 rounds, but they can not be considered reliable after 5,000 rds. The first indication of the trigger group wearing out is that the firing mechanism will lock up and you will not be able to shoot it unless you flip it to safe and then off to unlock it. Another indication is multi round bursts. The area where the Sears contact is very tiny so it stands to reason that they're going to wear out after 5000 rounds.

ALG triggers are a good replacement option.