Many years ago, as a competitive shooter in the military, we were taught that mixing ammo often changes the rhythm in battery and causes jams, stove pipes, etc. I don't know how truthful this is, but I have seen guns perform well, and then start stove piping, or jamming with mixed batches of ammo. When the shooter went back to one, or the other types of loads, the problem corrected itself. Most often this occurs in rapid fire.
The instructor was so convincing it caused me to stick with one load in a magazine.