I've now tried rebooting three times with auto-scan: Off. I wait 5 mins before activating PA and my music and settings are OK available, so to me it seems that @maxmp is correct when claiming that there is a delay in mounting the SDCard, probably due to UI 3.0/Android 11.
However my SDCard is available immediately after reboot in my file manager (X-plore). Weird....Are there multiple mounting points??