When closing a question (as a mod, so binding vote) using Close > Off-topic because ... > Other and entering a comment to explain why it was closed the question get closed but the explanatory comment does not get posted.
Example question: Unplugging and Plugging DisplayPort while PC is on
The comment was manually added by me after the question was closed as the comment added in the close dialog did not get added.
Screenshot for reference:
Possibly related issue: Comment not posted when voting to close as duplicate - Meta Stack Exchange