Cannot accept or reject subwiki candidates

STEPS TO REPRODUCE

1. Create one user on the Main wiki (e.g. U1)
2. Create a new subwiki with 'Both global and local users are available in the wiki' and Membership Type 'Any global user can request join but an admin must accept'
3. Login with U1
4. Go to Wiki Index
5. Click 'Request Join' for the subwiki
6. Click 'Send request'
7. Login with Admin
8. On the subwiki, go to Administer Wiki > Users & Rights > Users
9. On the 'Candidates' section, click 'Accept' or 'Reject'

EXPECTED RESULTS

The join request of U1 is accepted or rejected. All page elements are properly displayed.

ACTUAL RESULTS

There are no 'Accept' or 'Reject' buttons displayed, the 'Private Comment' text box is missing and the 'Admin's message' text box contains HTML code. Also, the page is missing left and right panels and footer (screenshots attached).

If other users request join for the subwiki afterwards, their names (or entries) are not displayed anymore on 'Candidates' section, only the first user remains displayed.

This issue could not be reproduced on XWiki 10.8.1.