Has only happened once so far. Was using M16A2 and L106. Fired entire mag from M16A2, started reloading, swapped to L106, fired some rounds, swapped back and completed reload. Next time I tried to fire nothing happened (unsure if empty gun click sound effect played). Swapping weapons back and forth didn't fix it, died before trying anything else like fire mode.
Can confirm happening regularly with all weapons. Seems like sprinting or changing weapons (may not be the case, seems like it happens without doing anything that would interrupt the reload sometimes) very close to the end of a reload (as in the animations appear complete) will completely undo it, even if the new mag was in the gun and charging handle had been racked. UI shows as having a full mag, but gun will go click.