Hi,
Thank you very much for the details, it helps us a lot!
So the error code was very strange, as I don’t recall we ever used those items it refers to. I went ahead, logged in and temporarily disabled the search plugin and checked the page again: https://i.imgur.com/LeiLfhX.png
As you can see, the search shortcode is not processed, because the plugin is disabled, yet the error is still there – which means it is not caused nor related to this plugin.
It seems to be printed just above the jet filters smart checkboxes element, so maybe it has something to do with that plugin I guess.