From just a few tests and skimming over the code, I can find a multitude of things going wrong.
The Redirect spell seems to be working fine, but the missiles as still moving below the ground a few frames after casting the spell. Because I'm not an expert with the missile system, I couldn't tell you why.
The Store Current Damage Damage Dealt function does not seem to assign the damage amount to the correct unit. Again, I could not tell you why, but the custom value of DamageEventSource is not consistent with the custom value of the units from the enters trigger. This bug might be related to another bug, which is that once the attacked unit dies, suddenly other units on the map start taking damage from the missiles.
The way you're determining the damage amount in the Store Current Damage Enters function is very janky and made no sense to me until I realized that you're deciding on each attack individually if you're replacing it with a relativistic missile or not, based on whether a unit with the Redirect ability is nearby. That is again a very janky implementation.
If you can make a good system that automatically replaces the attacks of all units on the map with relativistic missiles, that would actually be a useful resource. Then a mapmaker can do lots of things with it, and is not just limited to the Redirect ability.
You can use a single event to detect the attack damage, check if it's a ranged attack, and if so, store the damage amount, set the damage to 0, and replace it with a relativistic missile. There's no need for the convoluted stuff you have going on.
This will need major rewrites before it can get approved.
Awaiting Update