Samsung Galaxy 9(happened with my older phone too)
My Question or Issue
So I consistently have an issue where local files I put on my computer and then download to my phone will, for a few days, work, but then stop working all of a sudden, at which point I am unable to queue them and they will not play when in the list order or shuffle. I can still play them as normal by tapping them and the green download arrow still exists. The attached file is that of an mp3 taken from YouTube because it was recently removed from my region (the artist, nightcore reality is apparently attempting to get the spotify version re-allowed) and it is a visual representation of what is happening. Note this happens with almost all similar files at least once, and even worked with a 7 second dial tone I uploaded to see if it was an encoded thing with the mp3s I was using. All the methods I have found to fix this have resulted in only a temporary success, with the files still reverting given time.
This includes removing it from the downloaded playlist and the directory, re-adding it and then letting it download again.
Overall, if this has no fix it spells a horrible issue for spotify's premium service as the downloads and queues are the best part about premium imo