Comment, please 
System is VOLUMIO 2.238 on ODROID C2 , updated from 2.166
After boot ( re-boot) MUSIC LIBRARY is not available ( empty).
Selecting MY MUSIC from WWW interface restarts the user interface.
Looking at processes via SSH using TOP shows MPD is in “D” state. MPD is blocked for a long time, about 30 - 60 mins.
STRACE-ing on MPDs process shows intensive music library scan, with next repeated functions :
…
stat64("/var/lib/mpd/music/NAS/Music_01/T/The Subways", {st_mode=S_IFDIR|0777, st_size=0, …}) = 0
inotify_add_watch(13, “/var/lib/mpd/music/NAS/Music_01/T/The Subways”, IN_ATTRIB|IN_CLOSE_WRITE|IN_MOVE|IN_CREATE|IN_DELETE|IN_DELETE_SELF|IN_MOVE_SELF|IN_ONLYDIR) = 85346
openat(AT_FDCWD, “/var/lib/mpd/music/NAS/Music_01/T/The Subways”, O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 18
getdents64(18, /* 3 entries /, 32768) = 80
stat64("/var/lib/mpd/music/NAS/Music_01/T/The Subways/Festival", {st_mode=S_IFDIR|0777, st_size=0, …}) = 0
inotify_add_watch(13, “/var/lib/mpd/music/NAS/Music_01/T/The Subways/Festival”, IN_ATTRIB|IN_CLOSE_WRITE|IN_MOVE|IN_CREATE|IN_DELETE|IN_DELETE_SELF|IN_MOVE_SELF|IN_ONLYDIR) = 85347
openat(AT_FDCWD, “/var/lib/mpd/music/NAS/Music_01/T/The Subways/Festival”, O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 19
getdents64(19, / 3 entries /, 32768) = 96
stat64("/var/lib/mpd/music/NAS/Music_01/T/The Subways/Festival/The Subways-Oh Yeah.Mp3", {st_mode=S_IFREG|0766, st_size=4395028, …}) = 0
getdents64(19, / 0 entries /, 32768) = 0
close(19) = 0
getdents64(18, / 0 entries */, 32768) = 0
close(18) = 0
… and so on …
And after a while, MUSIC LIBRARY appear.
System VOLUMIO 2.238 on ODROID C2 , updated from 2.174 which is updated from 2.166 does not have this feature.