There is a bug in piwik where if browser_archiving_disabled_enforce=1 in the config, the VisitFrequency reports are not processed.
In 32015796d0a049d0118724dba240fdb56b4e1504: Fixes #4857 - When trigger=archivephp is found in the request, never disable archiving. this will make sure that visitFrequency, when calling VisitsSummary.get with a segment=visitorType==returning, then it will be pre-processed at all times by archive.php.
see also #2981
In c1f375e0309b9ff1de8508c53d94f25724560b02: Fixes #4857