How to fix this weird lag sound?

Question

I've been trying to figure out why the weird electronic lag sound is being created when two sounds are played together can anyone explain how to fix it.

I've tried my best to include comments for all important parts so that it can be of some help
https://sololearn.com/compiler-playground/WryBy4npCVtu/?ref=app

Until now I've figured out that the fade out part is causing that lag. But how to fix it?