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I take it you've tried listening to all of the songs on Stories, his 2015 album? Maybe check some of the singles, see if it's a B-side?
I have been listening to a lot of Avicii in the hopes that it was a case of right artist, wrong title, but no luck so far
Just to clarify is this https://www.youtube.com/watch?v=8rA5sueAkd4 "your" version or the "real" version
So I used to listen to this one song on youtube that was labeled as Chase the Sun by Avicii. I just went back to re-listen, and the video was gone. All the current results for Avicii Chase the Sun are a completely different song (probably the real "Chase the Sun"), and the song I'm trying to find was apparently something else entirely. Unfortunately, the song was instrumental so I can't just look up the lyrics. It was an upbeat electronic song comparable to Avicii's Holiday (here), and the video title was something like "Avicii Chase the Sun (NEW SONG 2015)"