Can't play some local files on iPhone Spotify, though they've played in the past

[WGRLA]

Problem: Some local files are not playing on the iPhone app, though they've played in previous versions. I'm even having problems getting all the songs from the same CD to be played as local files (some are, some aren't). I've tried various troubleshooting solutions I've found on here including creating new playlists, syncing via wifi, etc. The local files are transferring to iTunes on my phone, can play on the desktop Spotify, but simply aren't being found in the iPhone Spotify. Running iOS 9.3.2 and the latest version of Spotify.

[WGRLA]

Update: I tried to sync the same iPhone playlist that isn't finding all my local files to my iPad Spotify. Some of the local songs that didn't sync on the iPhone are syncing on the iPad. However, others aren't, including songs that are from the same CD where other local files are being synced. It's maddening.