As we don't have more information yet I couldn't reproduce it. Looking at the code it seems though like some metadata has an array in there. I didn't even quite know we had this renderer and from what I can see we're using it to convert a dataTableMap to a string. Not sure when and why. It should fix the warning though.
BTW I was seeing this error heaps of times in the logs.
Noticed it comes from twig when checking if an object is empty
in the dataTable twig
(could be a performance tweak to adjust this as the dataTable would maybe always return a string anyway)