I’ve recently started looking into a similar issue involving the Source and Target TagReqs, so this repro will be very helpful—thank you. Unfortunately, since aggregators aren’t USTRUCTs, there’s no straightforward way to ensure the GameplayEffect is retained in this scenario.
Your suggestion of adding something to the FGameplayEffectAttributeCaptureSpec is a reasonable workaround for now. That said, you’d need to iterate through all the modifiers in the captured aggregator and store the referenced GameplayEffects (or their specs) in something like a UPROPERTY-marked TArray.
I’m actively working on a solution, but it’s part of a larger task and likely won’t be available until that broader effort is complete.