[tofof]

Ok. Quick bug first: going to manage a playlist, then to 'grab last x videos' screen, then hitting 'cancel' sets the grab last to 10000.

Next up: Waited a day to post a log so I'd have something useful and could spot the service running, checking every 4 hours as I've got it configured, and downloading (or missing) files.

Service is running every 30 minutes, no problem there.

I have (among others) these channels and/or playlists:
https://www.youtube.com/user/LetsPlay/videos ---- successfully updated today, adding video 5KfPJc8p5R4 to the library.
https://www.youtube.com/playlist?list=PL...haxq__-Nvm ---- attempted to update today, but only grabbed the 50 oldest videos, and so didn't see the 2 new additions today (eps 51 and 52)
https://www.youtube.com/playlist?list=PL...MpARvHTdG6 ---- attempted to update today, but only grabbed the 50 oldest videos, and so didn't see the addition from 3 days ago (ep 101)

It appears the scheduled updates don't try and fetch more than 50 videos regardless of the 'fetch the x oldest' setting (mine is currently 5000).
It also appears that for channels, videos are ordered LIFO, but at least some playlists (like both of the above) are LILO.

Here is a playlist that's not LILO --
https://www.youtube.com/playlist?list=PL...gcww6QaImX ---- which updated yesterday, successfully adding all 7 new videos.

I think this now explains 100% of the improper behavior I've been seeing and answer why youtube-library seemed to sometimes work but not other times.

The log for the above period (26 hours or so) can be found at www.tofof.com/bag/kodi-1.log

Even doing manual 'update now' (or 'refresh playlist' followed by 'update now' to the Go and Let's Watch playlists doesn't successfully get the new videos (which are 51st or greater in the list).

Only an intial 1st-time scan seems to grab more than 50.