You can test that if you open a forum's topic at the real url,
https://www.bayonnais.com/board/viewtopic.php?t=13475
the server response return
Failed to load resource: the server responded with a status of 500 ()
before that any output is sent, and before the redirect, that should be done by the JS header code, when is detected that the page is not inside the WP page iframe.
You can also test this, if you do not want to force phpBB to load inside the iframe, and test:
Comment the line, into the overall_header added code
so
Code: Select all
//document.location.replace(href0);
(while you have set to Yes the Recompile Stale Template option into ACP)
then open the forum to the real url, and it will be loaded not inside the iframe.
And you'll get the same error 500, and blank page.
Cannot imagine at moment from where it could come out, but since others pages works, i assume it is a problem you created into template files? (if you changed it).
There is some extension that could interfere?
Overwrite/upload again the file viewtopic.php and the related template file so to assure that it is not corrupted?
Disable and test