I wondered whether you have solved this problem as I have the exact same symptoms with a 9422 .22LR. When cocking the gun with the lever, gun misfires. When manually cocking the hammer the gun always fires.
Firing pin is ok and hammer spring ok. The bolt is two piece held together by a pin. Upon removal I have cleaned everything and nothing appears worn. There appears to be a little play in the lever arm that moves the bolt back and forth ? Is this part of the design ?
My main attention is the rear part of the bolt. When cocking with the lever, this does not appear to move fully forward as per the front half of the bolt assembly sticking out by about 1mm. Upon manually cocking the gun after the misfire, this appears to jump forward making connection with front half and always firing !
Any expert advice, much appreciated ????