The 1919 uses a pull out type of belt, not a push through. When you load it the first round in the belt is just left of the extractor, The first pull of the handle advances the belt one cartridge, putting the round inline with the extractor. As the bolt slams forward, the extractor overrides the case and engages the extractor groove. The second pull of the handle extracts the cartridge from the belt and as it hits the rear end of travel the extractor pushes the round down into the T slot on the boltface, inline with the chamber. Forward travel chambers the round while of course the next round in the belt advances and is grabbed by the extractor.
As was mentioned, any fail to fire could be a lack of a chambered round, so the gun is cycled again to put a fresh round in the chamber, if the fail to feed was due to the belt not advancing then you are back to the same situation where you need two cycles to load the chamber. Some folks have been known to repeatedly cycle the gun until a live round is ejected, signifying the gun is feeding once again.
1919s are just what the name says, a gun first fielded in 1919, production for the .MIL ended in 1945. While the Israeli .308 conversion and other variants used new parts here and there, even those are mighty old so you have to deal with worn parts simply because of the age of the guns. So you get occasional misfeeds.