Interpretation of Stacktrace, What does this error mean?

After I insert a document into es, via spring data, i believe an indexing
phase is started called 'Dfs' (correct?) where a "query_binary" sort of a
Hash is retrieved.

this fails

Failed to parse source
[{"from":0,"size":10,"query_binary":"eyAnZm9vZHN0dWZmc0lkJyA6IDFmODMwZDk1LTQ0OTctNGFmZC1hNDVlLWE4MzQwYjg2ZTI2YiwgJ2xhYmVsTmFtZUlkJyA6IG51bGwgfQ=="}]]]

nested: JsonParseException[Unexpected character (''' (code 39)): was
expecting either valid name character (for unquoted name) or double-quote
(for quoted) to start field name

certainly I have no such ' single quote in this query or in the json
document:

{
"_index" : "foodstuff-lookup",
"_type" : "foodstuffslookup",
"_id" : "cae2d185-4795-4120-bb85-ebc5d1d5431a",
"_score" : 1.0,

"_source":{"id":"cae2d185-4795-4120-bb85-ebc5d1d5431a","lang":"it","displayName":null,"searchTerm":null,"preferrerd":[],"foodstuffsId":"1f830d95-4497-4afd-a45e-a8340b86e26b","labelNameId":null,"active":false,"stub":false,"intermediate":false,"additive":false,"alias":false}
} ]
}

so what is a possible interpretation of this error?

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