I have discovered what may have been causing everyone's inventories to max out. For some reason, whatever vehicle weapons you keep in storage will rapidly produce white ammo that seems to fill up by the amount of ammo the weapon normally has in its clip.

Its possible to delete theses via searching the all tab and scrapping the white ammo that suddenly appears. To prevent this from happening to yourself, I've found that scraping whatever vehicle weapons you don't need prevents the ammo from spawning. Any saves that already have too much of this are unfortunately, hopelessly lost.

Keep this in mind when using this option at all times, as failure to keep track of it WILL BRICK YOUR INVENTORY. BE WARNED.