Version 1.4.30
Occurred with half-elf warlock 4 and half-elf bard 4
I've noticed that Agonizing Blast sometimes doesn't apply properly. The invocation is definitely activated but occasionally isn't mentioned in the combat log and doesn't apply the bonus damage. I've found this is easiest to reproduce when using a bardic inspiration to succeed on an attack roll that would've missed, but I've also seen it when casting eldritch blast directly after choosing a new target for malediction.
Did the base (before the bonus was applied) damage kill the target? If so then that can happen whenever there is extra damage like from a Sneak Attack, Poison, Hunter's Mark, etc. If not then that sounds like a real bug.
No, the base damage definitely didn't kill the target. I'll try to get an example.
I've also noticed the reported bug behavior in similar circumstances.
I agree Agonizing Blast sometimes bugs out. It was definitely activated, and the targets weren't killed by the Eldritch Blasts. Note that on the event it doesn't add damage, the combat log also doesn't mention it, so the bug is at least consistent.