Unable to post reply for a forum post

Question

Recently i faced this issue often. I just want to post a reply for a forum question but unable to post it. When i click "Reply" button in the post, "Post a reply" section shown. After typing the reply, and click "post" button, it won't post the reply. It will still in the same page like below.

 

 

Any Moderators or technical staffs can you look into it?