I need mp3tag to extract the title and artist from the title alone. Then this needs to be added to the appropriate fields title and artist. This will enable me to fix the filenames easily as well.
I need mp3tag to pick up any occurrences of ft., feat. or featuring., remove any square or rounded brackets, change to ft. regardless of which sort of feat. was used originally and add featuring data to the end of the title within the artist brackets. So the title should be 'Rockabye (Clean Bandit ft. Sean Paul & Anne-Marie) rather than the original 'Clean Bandit - Rockabye [feat. Sean Paul & Anne-Marie]'
It's probably due to to a non-matching format string at "Guess values".
Look, Cold Water (feat. Justin Bieber & M0) doesn't include "%track%", " feat.", still has the featuring artist in parentheses and so on. So it really doesn't match your format string %track% %title% feat. %feat_artist%
From now on, please refrain from posting complex action groups that are not working and ask what's wrong. There are too many of your topics following this pattern already. It's not the purpose of this community and I find it disrespectful of people's time.
Instead, try to identify by yourself what's not working. Trace it down to the one action that doesn't produce what you're intending. If you don't understand why, you're welcome to ask about the detail and learn from that.
There is this quote, which I like in this context
Give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime.
I hope you learn to fish, given the vast resources that are available and the helpful community.