'Reply' button is missing from new posts

Occasionally in recent weeks I have been unable to respond to a new message because there is no 'Reply' button.

If I do something else, such as responding to another message or editing an existing message, then return to the unrespondable message, the 'Reply' button is there.  So, an intermittent fault -- the worst kind to track down.  But I issue the challenge anyway.

Happy Thanksgiving!

Regards, Jon Summers