To reproduce set your limit in the visitor log eg to 5 and then click on the next page. You will see in the Live model method when it fetches the data that it will be actually fetching 7 entries.
It does a
$limit + 1 here: https://github.com/matomo-org/matomo/blob/3.11.0/plugins/Live/Visualizations/VisitorLog.php#L57
and then another +1 here: https://github.com/matomo-org/matomo/blob/3.11.0/plugins/Live/Model.php#L43
This way you might skip in the end a visitor? Anyway, it should only do one of the plus ones. Probably the one in the visualisation can be simply removed.
On the Administration page (index.php?module=CoreAdminHome&action=home&idSite=1&period=week&date=today), I'm seeing four of these:
WARNING: /matomo/plugins/Live/Visualizations/VisitorLog.php(225): Notice - Trying to access array offset on value of type null - Matomo 3.13.1 - Please report this message in the Matomo forums: https://forum.matomo.org (please do a search first as it might have been reported already) (Module: Live, Action: getLastVisitsDetails, In CLI mode: false)
Is this related? If not, I can create new bug. I'm seeing this after upgrading to 3.13.1 (PHP 7.4).