For those who suffers from 'playlistNotFound' when trying to add to 'Watch Later' - i may have stumbled upon a potential workaround
1. go to YouTube plugin and add 'Watch Later' to kodi favourites
- if you do not do that then you won't be able to access it after the workaround is applied
2. shut down Kodi
3. open file ".kodi/userdata/addon_data/plugin.video.youtube/access_manager.json" in a text editor and check if "watch_later" key has value " WL" (note the space in front of WL)
- remove space to make it:
json:
"watch_later": "WL"
and save
4. start kodi again and check if you can use usual context menu to add to 'Watch Later' without error
- note: at this stage standard Watch Later folder under Youtube addon will stop working, however - the one we added to kodi favourites on step 1 should still work
Not sure if this is universal workaround, but works for me (Youtube Addon version 6.8.4) so I figured it may help someone.