Another possible Jump phenomenon: Jump borers.
Just as ship borers in the seas of ancient Earth bored into the hulls of wooden ships, weakening the wood, so Jump borers corrode pits and holes into the surface of a starship.
It's not really known if the effects are produced by something in jump space, or merely by the effect of the jump bubble, but the effect is very real. After a jump, the hull of a ship will have small corroded pits or even neat little holes (also corroded) in it. None of these holes goes too deep, but it does eventually weaken the hull - particularly if too many accumulate in one area.
Use of special materials on the outer layer of the hull can prevent most problems. And, fortunately, they don't like the taste of lanthanum (assuming it is critters). Unfortunately, they have been known to bore their holes right next to the lanthanum grid, sometimes cutting partway into it. It has caused occasional failures when trying to enter jump.
Those who think it is a creature believe that - just like its Terran aquatic counterpart - it is a filter feeder: feeding off the hydrogen and energy of the jump bubble. Though jump physics scientists scoff at this idea, claiming it is merely a result of flaws in the jump matrix causing hull erosion, old space hands insist they have seen the borers on exterior visual sensors during jump.
Some folks say the borers drop off when the ship exits jump space, and reattach to the next ship that enters. Others insist the borers remain when the ship returns to normal space, but are undetectable, remaining in some sort of jump phase with the ship. They claim the only way to scrub the borers off is to skim a stellar corona, or dive into a gas giant. (There are claims that a plasma rifle played over the skin of the ship will work, as well.)
No matter the cause, hulls should be inspected frequently, as the defects can cause loss of protection from inter-planetary material bombardment, as well as armor effects against weaponry.