On a self hosted matomo, I irregularly have the following warning on the home page (index.php?module=CoreHome&action=index&idSite=1&period=range&date=last7#?period=range&date=last7&idSite=1&category=Dashboard_Dashboard&subcategory=1) :
WARNING: /core/Tracker/PageUrl.php(396): Deprecated - substr(): Passing null to parameter #1 ($string) of type string is deprecated - Matomo 5.6.2 - Please report this message in the Matomo forums: ``https://forum.matomo.org`` (please do a search first as it might have been reported already) (Module: API, Action: get, Method: VisitsSummary.get, In CLI mode: false)
When it appears, it is listed 4 times in yellow panels before the page’s content.
I could not find any related logs.
It appears irregularly : sometimes 2 times in a row, sometimes it doesnt appear for a lot of calls.
I am seeing similar warnings on a self-hosted Matomo instance. The warnings appeared right after updating from Matomo 5.6.1 to 5.6.2 and they are still present in the newest version (5.7.1).
A sample of the warnings from the logs:
WARNING CustomDimensions[2026-02-06 12:46:30 UTC] [1826510] /data/matomo/core/Tracker/PageUrl.php(396): Deprecated - substr(): Passing null to parameter #1 ($string) of type string is deprecated - Matomo 5.7.1 - Please report this message in the Matomo forums: https://forum.matomo.org (please do a search first as it might have been reported already) [internal function]: Piwik\ErrorHandler::errorHandler(),#1/core/Tracker/PageUrl.php(396),#2/plugins/CustomDimensions/RecordBuilders/CustomDimension.php(229),#3/plugins/CustomDimensions/RecordBuilders/CustomDimension.php(80),#4/core/ArchiveProcessor/RecordBuilder.php(99),#5/core/Plugin/Archiver.php(217),#6/core/ArchiveProcessor/PluginsArchiver.php(186),#7/core/ArchiveProcessor/Loader.php(328),#8/core/ArchiveProcessor/Loader.php(201),#9/core/ArchiveProcessor/Loader.php(180)
It looks like #2/plugins/CustomDimensions/RecordBuilders/CustomDimension.php(229) was last changed in the pull request “Improve rollup ranking queries #23868” (commit 7c16e03b6bbd357d92dd3a32ee055ed0bc7e83d7). According to the changelog, this pull request was closed in 5.6.2.