Hyperspace 101 is in session.
To put it in the simplest terms, hyperspace engines don't really "move" a ship through hyperspace. The process is called "jumping" because that's what the engines really do. Their function is to push the ship into and out of hyperspace, to breach the upper-dimensional boundary to get in, then push the ship back into normal space when it gets where it's going. Propulsion in hyperspace itself is a different matter. When it initially breaches hyperspace, normal engines just push the ship into a course and speed, then count down a set time before reversing the process. That's why a ship has to be physically pointing in the direction in normal space it wants to go when it jumps into hyperspace.
When a ship's engines breach hyperspace and send the ship in, that ship is invested with a certain amount of "velocity." It's not really velocity, but let's call it that for now. The ship literally just coasts on that "velocity" without resistance through hyperspace, and after a pre-determined amount of time, the ship's computer automatically uses the engines to transition the ship back into real space.
Think of it as water in a whirlpool when water drains out of your tub. No matter how fast or slow an object is going when it gets there, the whirlpool regulates its velocity once it enters, and then it enters the pipe below at a set speed dictated by how much water is draining into it. This is a very rough and not entirely complete metaphor for what happens when a real space object "drains" into hyperspace, but it's good enough.
Karinne hyperspace engines can actually move a ship in hyperspace, changing course and speed, and this is one reason why Karinne engines don't suffer a relativity delay. The actual elapsed time of a normal ship and a Karinne ship in hyperspace is NOT the same, it is just the perception of the people on board that makes it so. When a Karinne ship enters hyperspace, the engines "burst" and invest the ship in a very specific amount of hyperspace velocity that syncs the ship with real time, and then it travels to its endpoint destination. It takes two days for the Imperium to jump from Makan to Karis in real time. The crew on those ships perceive only about maybe 17 seconds of real time, but in actuality, they spend about a second longer in hyperspace in "hyperspace time," which translates to a real time delay. This difference in velocity is very small, but it has a tremendous impact. Hyperspace is a realm where true speed alters time itself at an exaggerated level, because there is no real time in hyperspace, and there is no "velocity" in hyperspace. "Time" is a subjective quantity linked directly to speed. A Karinne ship does not really go faster in hyperspace, it compresses pure time as an independent variable not linked to the space-time continuum to simulate velocity, and it can do that because in hyperspace, space and time are NOT directly linked. Because Karinne and Consortium ship engines can actively induce velocity while in hyperspace, they compress time and therefore can move through hyperspace in real time.
You might ask "if ships can manipulate time itself, why can't they go "faster" and arrive at a destination faster than in real time?" That's a very good question, and the Karinnes labored to solve it for a very long time. The simplest solution is that even though time is an independent variable in hyperspace, the three dimensional object trying to alter time is limited by the dimension from which it entered hyperspace. It cannot compress time at a rate faster than time flows at the point where it entered hyperspace, it can only compress hyperspace time up to the point where it matches time at its point of entry. And since Karinne ships must be moving at a very slow velocity to enter hyperspace, they can't exploit the idea of accelerating to near-light speeds and then making a jump to let them traverse the entire galaxy in under a second.
Ships need their engines to breach the barrier of hyperspace on both sides of their trip, and that's why a ship can become trapped in hyperspace. If its engines fail while in hyperspace, then they can't get out, and as someone else pointed out, the disorienting effect of hyperspace makes it impossible to effect repairs. How they get out is simply to "stop" in hyperspace. It's that subjective induced velocity that keeps them in hyperspace, so to get out, they simply shed that induced velocity. Three dimensional objects in hyperspace are like paper airplanes...if they have no velocity, they can't stay airborne. Inertia seems to exist in hyperspace, and there is no sense of friction to naturally slow objects, so a ship that fails to jump out, that does not shed its velocity, will continue on until some outside force affects it and causes it to "fall" out of hyperspace.
The reality the Karinnes don't know is that there IS an eventual slowing of an item and an ultimate drop out of hyperspace without engines, but that takes about a year, and sends the vessel literallly to the other side of the universe.
There are hyperspace features that can force a ship out of hyperspace early, robbing it of its "velocity" and dropping it to real space. A teryon current is one such event, a river of pure energy that, when a ship hits it, it stops it dead and causes it to drop into real space. Hyperspace wrinkles, distortion in the fabric of hyperspace, also have this effect. Think of it as a "speed bump" in hyperspace, and it robs a ship of its "velocity" and makes it drop.
This is how the interdictor works. It generates artificial distortions in a very small area in hyperspace, which translates to a sphere a light-year in diameter in real space. This distortion robs real objects of any induced velocity and forces them to drop back into real space. These distortions are ACTIVE, they are like ripples in a pond created by a pendulum dipping into the water, radiating away from the source. This effect overcomes engines that can even move in real time, engines that can invest a ship with its own velocity. If not for the fact that a real object drops back into real space instantaneously when it loses its velocity, the interdictor could probably push ships back through hyperspace.
It will have one effect, though. Ships that enter the area of its effect at an angle or tangent to the effect aren't pushed back into real space, they are instead deflected, altering their course. The result is that when the drop back into normal space, they aren't where they're supposed to be.
The interdictor will have no effect on Karinne technology or communications outside of preventing them from using hyperspace engines to reach Karis.