This is typically seen when mpd scanning comes a cross a file/files that are corrupted in some fashion, or maybe certain file types (not too sure about this).
In your log, there are a number of tracks skipped eg.Saudade/13. One note samba(a.c. jobim).mp3, but mpd continues indexing ok.
There are a lot of tracks in ‘Recycle Bin’ that mpd doesn’t like … you would be better to totally remove this folder, or at least get Mpd to ignore it’s contents (have a read of how to exclude folders from Library update).
A.R. RAHMAN (SIGNATURE COLLECTION–2) All tracks give rise to a ffmpeg warning:
ffmpeg/mov,mp4,m4a,3gp,3g2,mj2: max_analyze_duration 5000000 reached
You would have to try a Google search to see if this is critical or just advisory.
No file headers on some tracks eg. Dhamaaka Hits - 06.
At this point, I have stopped looking at your log.
I suggest that you clean up your USB drive contents by isolating the files that mpd is skipping (as detailed in the log), until you get a completely indexed drive. You can then try reintroducing isolated tracks and check that they are successfully indexed, even if mpd is complaining a little.
Good luck with what looks to be a big job.