visitors don't appear on subforums

[.m.]

check forumdisplay template of the theme - does it consist of code {$usersbrowsing}

also check the content of forumdisplay_usersbrowsing template

<span class="smalltext">{$lang->users_browsing_forum} {$onlinemembers}{$onlinesep}{$invisonline}{$onlinesep2}{$guestsonline}</span><br />