Well, guess what. My IntelliJ was actually a bit too old, and that’s why the plugin was stuck on 1.4.17 
. Is it really necessary to force the update to a newer IntelliJ for 1.4.28?
Anyway, I updated and indeed, I can confirm that the indexing issue is gone! Hooray for that! Good work + thank you!
Unfortunately… I ran into this now: Weird inspection errors · Issue #1147 · HaxeFoundation/intellij-haxe · GitHub