Possibly the rivet that connects the gas rod to the bolt carriage
has backed out into the gas chamber while firing.
Field strip the weapon. After you remove the bolt cover and
return spring, see if you can remove the bolt carriage and gas rod
by gently drifting it backwards with a screwdriver handle.
Also, many "new"(?) AKs have dried up grease or Cosmoline in the chamber.
Take a large bore mop, soak it in hot water and degreaser, put two
sections of a cleaning rod onto a drill, and swab out that chamber real well
on low speed,(clockwise rotation) from the breech end of the rifle.
WASRs are one of the standards of the industry, IMO.