In continuation with issue topic: https://www.phpbb.com/community/viewtopic.php?p=13991266#p13991266

There might be problem with routing, which does not take in account "Force server URL settings:". That leads to incorrect url paths in extension generated links, that are using routing system, like http://domain.com/path_to_phpbb_root/extension_something instead of http://domain.com/extension_something like all other phpbb functionality does with enabled Force server URL settings.