I agree with all the advice given so far. I'll add that your crimps aren't made correctly. Much like a slip knot, the sleeve should be tight against the eye that the cable is being crimped to. If it's not, the only thing actually holding it in place is the stiffness of the bend in the cable. That will let go eventually.
I disagree though that the cables need to be super tight. Extra tight cables do put a side torque on the output gear of your servo that it was not designed to handle. Premature gear wear will result. Honestly, the cables only really need to be tight enough to not add any more slop that what the servo gears and deadband of the servo add. It's not scientific, but I set mine up to give me a low bass note "thunk" sound when plucked. No sound is too loose, and any note you'd find on a guitar is too tight. Ideally, I look for the note to stay the same through both directions of the servo's travel, but I accept a slightly lower thunk at the extreme ends. I set mine to the loosest setting that gives me a thunk, then check for slop. That's with straight shots for both wires. Anything they touch adds an extra variable in the tensioning.