The existing comment text is not visible when editing the comment

Prerequisites: The Forum Application must be installed.

STEPS TO REPRODUCE

1. Create a forum and add a topic
2. In the topic, add an answer and a comment to the answer
3. Click the "Pencil" green Icon to edit the previously added comment

EXPECTED RESULTS

When entering the edit mode for the comment (regardless of the editor), the existing text of the comment is visible, so the content can be partially modified/deleted.

ACTUAL RESULTS

When entering the edit mode for the comment (and the editor appears), the existing text of the comment is not visible. Also, if typing another text and saved, the existing comment is fully overwritten.

Also, when click on "Pencil" green Icon to edit any comment, the following warning appears in console:

2017-07-13 11:58:10,765 [http://localhost:9515/xwiki/bin/edit/ForumCode/CommentTemplate?xpage=wysiwyginput&token=$services.csrf.getToken()] WARN  o.x.c.i.DefaultCSRFToken       - CSRFToken: Secret token verification failed, token: "$services.csrf.getToken()", stored token: "c30V5LIZ53dJLsW2ZpM5xw"

Note: There are also some issues regarding the editors displayed in comments. See XAFORUM-234 and XWIKI-13828.