Why can't I reply in my post

[Speedwell]

I have posted about a problem with ARC when using the TT hub.  There has been a reply and I want to reply to the reply.  I have replied successfully in the past to other posts but this time the reply button is missing.  Can anybody tell me what is going wrong

[ferguson]

If you start typing in the reply field it will work. Or to reply to a specific poster click on the blue arrow at the end of their post.