Not completely familiar with this error but perhaps try introducing your “all __ chunks” using the ontology option instead of as a variable. the semantic search block you’re using is definitely expecting an object set.
When I select Object Set of allChunks as a variable it either shows as a String or as Unknown (see screenshot) ; the Property to Search shows nothing (‘embedding’ can’t be selected).
I did not fully followed the tutorial instructions as I did not drop the ‘response’ column, because I did not see the reason why dropping it and thought that could be useful for later…