After I have added a comment to text and then delete it the text remains blue and underlined. I have tried the fix of coping to another document (and indeed the blue underlined goes) but when I copy it back into scrivener the blue underline returns. Please help! Thanks
This is a known bug; see this thread for a workaround:
[url]https://forum.literatureandlatte.com/t/removing-comment-creates-a-fake-hyperlink/48186/1]
(For future reference, the Using Scrivener forum is a place to post tips and techniques; please use the Mac technical support forum to ask for help, as there aren’t a lot of people hanging out here. 
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Thank you. I will post there in future.