the Music app is a fork of Twelve. It’s catalogued in the LineageOS bugtracker - Twelve - Crash upon clicking "Add or remove from playlists" (#10137) · Issues · LineageOS / issues / android · GitLab
from that logcat.txt:
E AndroidRuntime: FATAL EXCEPTION: main
..
E AndroidRuntime: java.lang.ClassCastException:
org.lineageos.twelve.models.Provider cannot be cast to
org.lineageos.twelve.models.ProviderIdentifier
when adding, is there anything special (sdcard or remote file) about the origin of the files?