Just setup a new instance on a new server and problem persists there as well. For good measure i also tried it with apache. Problem is only in the app. Mobile browser and Desktop browser are all caching the m4a files. So when switching a channel it does not reload all the stuff from the server again.
meanwhile big images (3mb) are definitly getting cached in the app, so no new request is send upon channel switch.
Probably no one ever noticed because with normal use cases like 5 30sec recodings its pretty much instant because its less than 2mb getting loaded in this case.
Another solution would probably also not loading all the audio files upon entering, just loading the one that gets clicked.
hope someone has some time checking this problem. Maybe I have some time for compiling the app so I can do it myself.