How I get rid of exclamation mark near thread at slack? I cannot find the unsent message

I get exclamation mark near thread. The point is unsent message but I cannot find it.
When I hover on exclamation mark I can get snippet of the unsent message, but when I search for it, I cannot find it (probably because it not sent.
This is any solution?

I read twit from slack – but it not help
https://twitter.com/slackhq/status/1012994511293861894?lang=en