(I'd post more flavor text for my cosomusic posts, by the way, but it seems CoSo arbitrarily decides sometimes that having anything more than a title and artist is malicious, or just makes the post button shy. 😅 )
If you're using quotation marks or other special characters try removing them and see if you have trouble.
@Shelter I thought the same and tried to work around it, but I always put the song name in quotes and use a long hyphen, and that passes. Even adding one sentence with no special characters can bork it. I'll have to experiment more.