The sustained charge mod is completely nonfunctional with all of the weapon types it is supposed to benefit, no matter how fast or how many enemies you kill back to back. Having more or less sustained charge mods does not fix the problem.
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You're not getting a charge because without a mod to use said charge on, you can't be charged.
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Your Titan doesn't have any mods that use Charges of Light (yellow), this is why you are not being Charged With Light: at least one green and one yellow mod are required to be equipped at the same time.