Running a recently-reset OP5 with OxygenOS, and the song position is always the same as the duration. The "Music Playtime" formula for progress also resets to 0 every time my music is paused, and doesn't reset to 0 on track change. I have tested this and the same issue occours with AIMP, Phonograph, and Retro Music.
These issues are unfortunately related to the music player, you can test Spotify, Google Music and others and you will see that those works properly
I'm inclined to believe that it's a problem with my device, as 1) Others with different devices have reported that these players work fine, and 2) I refuse to believe that Phonograph doesn't have KLWP support.