Following error happened on
"message":"Cannot unset string offsets","file":"plugins\/CoreVisualizations\/JqplotDataGenerator.php","line":106
Haven't tried to reproduce myself so not sure if it is an easy fix or not.
Can be easily reproduces on demo: https://demo.matomo.org/index.php?date=2018-03-18&viewDataTable=graphVerticalBar&module=VisitTime&action=getByDayOfWeek&widget=1&columns_to_display=nb_actions,nb_uniq_visitors&idSite=7&period=week
But that might be by design.
columns_to_display is handled as array, but a string is given in URL. Correct would be
Need to investigate if we generate such broken urls anywhere in the code...
(It is also reproduced several times by customers)
Do you know a way to reproduce it in Matomo without calling the API directly (with incorrect params)