If the ammo worked for two years and now it does not, I would likely rule it out. Try some factory ammo to be sure. Your rifle has a free float forend, I presume?
It sounds like the action is short cycling.
You need to look at the gas tube where it connects with the front sight base/gas block. Look for carbon build up on the exterior of the tube indicative of a gas leak. If you see much carbon on the tube, replace the
Clean the inside of the tube by flooding it from the receiver end with a good solvent like Shooters Choice. Stand the rifle up on the muzzle and dribble solvent into the tube. Get some of the special long pipe cleaners made to clean AR gas tubes. Soak an hour or so then swab out the tube. If the pipe cleaner comes out green, you may want to consider removing it and cleaning it more thoroughly.
Check the bolt carrier group. Make sure the gas key is tight. The allen screws can loosen when not properly staked. Torque is 40 INCH/pounds.
Check that you do not have a broken or missing gas ring. Position of the gaps is NOT important (contrary to urban legend). Remove and clean the gas rings and their groove. Leave them dry. You may consider replacing them as they have a life expectancy of about 3000 rds.
Finally check the buffer, spring and retainer. Make sure they are not binding. Remove buffer and spring. clean the tube looking carefully for debris.
Your load sounds very reasonable. I doubt a small base sizer die is needed.