The AK is basically a balancing act between the gas from the cartridge when fired & the recoil spring. Since yours worked to start with, then started short stroking, something has gotten out of the balance.
Gas ports usually don't just plug up, so look @ that last as you strip the gun. Open the top cover after clearing the gun & check the spring to make sure it is intact. Then see if the bolt carrier slides back & forth easily & is not dragging on the rails with the spring removed (it will drag on the hammer). To stop it from dragging on the hammer, cock the hammer & hold the trigger down & it will lock the hammer out of the way. If that shows nothing is slowing down the bolt carrier, remove the top piece of the front handguard/gastube & use a flashlight to look down into the gas block to see if it is clear & nothing is in it. Shining a flashlight into it & looking down the barrel from the muzzle side will let you see if it is clear.
If every thing seems to be fine, reassemble the gun & oil the rails where the carrier runs & the bolt & see if it will eject a round.