Expanded comment (thanks to Ere Maijala for the suggestion).

config/vufind/config.ini

@@ -1142,7 +1142,10 @@ treeSearchLimit = 100
 ;universal = false
 
 ; Uncomment this section and provide your Piwik server address and site id to
-; enable Piwik analytics.
+; enable Piwik analytics. Note: VuFind's Piwik integration uses several custom
+; variables; to take advantage of them, you must reconfigure Piwik by switching
+; to its root directory and running this command to raise a default limit:
+; ./console customvariables:set-max-custom-variables 10
 [Piwik]
 ;url = "http://server.address/piwik/"
 ;site_id = 1