So, tried again from scratch - all damn day... (just erased entire configuration and not reinstalled)
Adding my NFS shares again as prescribed here ( https://libreelec.wiki/how_to/mount_network_share?s[]=nfs#tab__nfs )
Ensured all permissions were as they should be on the files - ruling out a permissions issue on individual entries
Enabled logging, added the required share and let it scan... using Universal Movie Scraper.
It hasn't got past 'A' yet but seems a lot better.
What did I do prior to this...
1) find . -type f -iname \*.nfo -delete
2) find . -type f -iname \*.jpg -delete
3) chown across all files recursively to ensure that all files were owned by the same user/group
4) I turned off the damn metadata settings in Sonarr and Radarr (they made their own .nfo files and that seemed to be the blame)
5) Enabled SMB - never got around to using this but likely faster than NFSv3
6) On my NAS I enabled Squash to map all users to admin (but I'll likely turn this off)
7) Found numerous freaking bugs in Radarr - however all unrelated to this
And after 40 minutes it still is pushing through 'A' and seems to be happier. If anyone is interested, debugging is on and I'll share an updated file - via Google Drive again - it is sizeable already! I'll leave it for a few hours and 'see what happens' before I close this issue out.