When setting an AnimNotify to an AnimationSequence, this AnimNotify can be triggered multiple times when only set once. This issue only happens when the mentioned AnimationSequence that contains the AnimNotify is reproduced inside the Sequencer.
Once the AnimNotify is triggered, it might still reproduce again the AnimNotify after some time. After some debugging, we've seen that FAnimNotifyQueue::AddAnimNotidiesToDestNoFiltering is called everysingle time the Notify is going to reproduce again.
It is a bit hard to reproduce, but the user was able to give an updated reproduction project that triggers the issue. Just open the LevelSequence and reproduce it. You will see that the AnimNotify gets triggered correctly, but before the MM_Idle Animation ends, the AnimNotify triggers a second time without being any second AnimNotify set in the AnimationSequence.
With the repro project:
1- Download and open the last repro project the user mentioned.
2- Open the LS_Test.
3- Reproduce the LS_Test. You will see that the message of the AnimNotify gets printed multiple times, not only when it was set.
Without the repro project given by the user:
1- Add the ThirdPerson feature content.
2- Create a blueprint AnimNotify that prints a random message. Open MM_Idle and set the anim notify.
3- Create an AnimInstace c++ class. Reparent ABP_Manny from it.
4- Create a Blueprint Character. Set the SkeletalMesh to SKM_Manny and the BLueprint to AnimationBlueprint -> ABP_Manny.
5- Create a LevelSequence. Add a BP_Character as a spawnable inside the sequencer. Add an animation track with the animation that has the AnimNotify.
6- Reproduce the Level Sequence and see that the message might get printed more than once.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-223114 in the post.