When the "out-animation" starts it should fire the aos:out:customEvent
When the "out-animation" starts it fire the aos:in:customEvent
change line 49 inside handleScroll.js from:
fireEvent(aos:in:${el.options.id}, node);
to:
fireEvent(aos:out:${el.options.id}, node);
I've also noticed this bug; i managed to get the out event working but still the aos:in fires..

It seems that your correction solves it but it hasn't been corrected yet :(
I already created a pull request to fix this issue, the author of AOS hasnt responded yet. Pretty sure he will at some point, can't wait to use the official repository again. Meanwhile i forked the project and fixed the bug there: https://github.com/AndTheGodsMadeLove/aos
If you are just looking for a minified version with the fix you can find it here: https://samuelweber.at/aos/dist/aos.js
Would love to see this merged and released so can be used as an npm-asset
Most helpful comment
I already created a pull request to fix this issue, the author of AOS hasnt responded yet. Pretty sure he will at some point, can't wait to use the official repository again. Meanwhile i forked the project and fixed the bug there: https://github.com/AndTheGodsMadeLove/aos
If you are just looking for a minified version with the fix you can find it here: https://samuelweber.at/aos/dist/aos.js