Causal Correction

FTL travel violates causality. By default, it just does that. Now, you would think that that disables it entirely. But FTL travel has been commonplace for that last 200 years. Obviously, there's something that allows it, right? Well, there is. A very poorly understood but mostly predictable phenomenon, it is, at simplest, the universe fixing itself.

Skejon: "So, what's wrong with it?"
Jon: "You want a thorough explanation?"
Skejon: "Sure."
Jon: Sighs. "The mechanism that keeps the negative matter in its container is nonfunctional, and the electromagnet controlling passage to the drive itself is being constantly powered. Also, the main drive is in continous projection mode, and trying to turn it off improperly would result in the isolated space of non-warped spacetime collapsing on the ship. That would cause the warping of spacetime to travel across the ship, tearing it apart on the quantum level. On top of that, such a rapid and asymmetrical shift from superluminal travel to subluminal would end up in causing all sorts of unpredictable causal violations, and thus also invoking the universe's strange methods of fixing itself, which would at best do nothing and at worst erase all of us from reality. Even if we survive that, we'll still be stranded in space far from the nearest human system with limited fuel."
Skejon: "I understood around half of that, that's not good, right?"
Quaken: "I have no clue."
Jon: "The drive is stuck on and if I don't turn it off carefully we will certainly die, at best."

Yes, I reused this quote again, because it 1. fits, and 2. is good.

Cause

What exactly causes the phenomenon is entirely speculative, at best. The existence of a corrective force of sorts has had quite the impact on religion, the little there still is, but the effect largely seems to follow logic and be caused by an FTL drive, as difficult to decipher as that logic is. The foremost speculation involves primarily the nature of the FTL bubble, and its warping of spacetime and technically going faster than light in a literal way, and thus experiencing some wacky time dilation effects.

Effect

The phenomenon only really manifests when one touches a powered field actively warping spacetime. This is, of course, not that easy, since that bubble field will be going at at least several times c. But it can happen, and in fact, the warp doesn't start accelerating until a few moments after activation.
During this window, if anything at all enters the bubble-field, it will be subject to causality correction. Exactly why an unmoving bubble of realtime surrounded by a warp causes this is unknown, but speculation is aplenty. This also applies during flight, as various bits of debris and particles otherwise potentially harmful don't do anything to the ship, as they are also subject to the effect.
So what does causal correction actually do? Well, it varies. The effect seems to depend on the objects mass or velocity, the higher one is, the more likely the object is to suffer more severe effects. For example, a human ending up passing through the bubble's barrier will most likely be completely removed from the universe, with no trace left whatsoever. The same happens to the many miniscule particles a spaceship gets hit by during FTL travel. Of course, this doesn't always happen. It is a near-certainty, but not always. There are reports and test logs of people passing through the barrier still in existence, though often not unscathed.
Sometimes, however, if something particularily big, like a planet or another ship passes through the barrier, if partially, the field collapses, shearing the ship apart on a molecular level, as the page quote says.

Effect on space travel

While being a massively inconvenient and potentially dangerous phenomenon, it is largely predictable. As long as nothing comes into contact with the ship while the drive is powering up, nothing will happen an overwhelming majority of the time. As such, FTL drives come with basic safety protocols anyone flying a ship capable of it should already be aware of. This has allowed FTL travel to be a thing at very minimal risk.

Type

Natural