This may be related to the amount of hash tags combined with the minimum length of the title.
In other words, let's say there's a minimum of 15 characters in the title (a title shorter than 15 characters won't be very readable to users, after all). If the combined length of your hash tags and built-in Twitter link shortener length is (140 - 15) 125 characters or more, then the tweet will have a length over 140, and fail to post.
The combined length of your hash tags is approx 45 characters, plus 25 characters for the t.co URL, leaving 70 characters. Are any of the titles of your threads longer than 70 characters? If so, there may be a problem with the character counter somewhere, as it should trim the title to stay within the character limit.