Users land to a (broken) page with missing elements when log-in from Comments section

STEPS TO REPRODUCE

Preconditions: Have a page created with Comment rights for Unregistered users.

1. Login as Admin
2. Create a page (e.g. P1)
3. Click Administer Page > Users & Rights > Rights: Page > Users
4. Tick 'Comment' for 'Unregistered Users'
5. Logout
6. Go to the page P1
7. Click 'Log-in' from Comments section
8. Fill the credentials for Admin or for an existing user
9. Click 'Log-in'

EXPECTED RESULTS

After login, Admin/User is directed to Comment section of the page P1 (where it was previously).

ACTUAL RESULTS

After login the user lands on a page which is missing most of XWiki page elements (like Panels, Navigation bar, footer). Only some buttons are displayed (but wrongly placed), which when they're clicked nothing happens.

The page URL is the following:

http://localhost:8080/bin/get/Pag1/WebHome?xpage=xpart&vm=commentsinline.vm

At this point, the Admin/User must manually navigate to an existing wiki page from URL, however, it is logged-in.

The issue could be reproduced also on older XWiki versions (tested down to XWiki 10.11.11).