The slow firing and "jamming" was a bug they introduced during one of the patches in TDB. It may be something else, but it could just be that glitch. It should go away with one of three conditions: reloading, swapping the weapon out with another secondary and re-equipping it or going to orbit and back. It was occasionally very persistent. I have always found the flavor text about it being a "doorway" interesting. Though, I assume that's referring to the re-firing missed shots via a vex-tech time loop within the weapon. Looking at the video, it does look like the glitch. Although it's extra glitchy with the variable rate of fire. However, it sped up its shots when it was aimed in several different directions, not just when you aimed at one specific point.