Music no longer remembers where i left off

When i'm listening to a playlist or album from the music app on my bluetooth (note i'm listening to mp3s that i downloaded onto my iphone), if i pause for longer than a few minutes, what i was listening to is gone (it says "not playing" in the app.) If i press play, it starts to play my entire library.

This is frustrating when i'm listening to an audiobook and i have to try to figure out where i left off. This started happening about 6 months ago. Prior to that, i could pause overnight and it would still pick up where i left off.

Does anyone know a solution to this? Note, i am on IOS 13.5.1 on an Iphone SE.