For background, see this issue.

When a statement is written having a value that is a quantity, and that quantity is a whole number, the WD Query Service binds a datatyped literal value like "4"^^xsd:decimal . This is the canonical representation under XML Schema 1. However, under XML Schema 1.1, the canonical representation is now "4.0"^^xsd:decimal .

The practical implication of this is that if a federated query to the Wikidata Query Service is made from a service like Apache Jena that supports XML Schema 1.1, variables that are bound to the same whole decimal number locally and on the remote endpoint do not match.

I realize that Blazegraph is no longer supported by its developers, so I don't know how difficult it would be to update the handling of whole decimal numbers to XML Schema 1.1

To reproduce, load this triple locally in Jena into the graph http://journals:

wd:Q97446840 wdt:P2896 4.0 .

Perform the following query

prefix  wd:  <http://www.wikidata.org/entity/>
prefix  wdt:  <http://www.wikidata.org/prop/direct/>

   SELECT DISTINCT ?value
    WHERE {
    GRAPH <http://journals> { 
    wd:Q97446840 wdt:P2896 ?value.
  }
}

The result is "4.0"^^xsd:decimal

Now in Jena perform the following federated query:

prefix  wd:  <http://www.wikidata.org/entity/>
prefix  wdt:  <http://www.wikidata.org/prop/direct/>

   SELECT DISTINCT ?value
    WHERE {
    SERVICE <https://query.wikidata.org/sparql> { 
    wd:Q97446840 wdt:P2896 ?value.
  }
}

The response is "4"^^xsd:decimal . If you combine the two queries into a single query and perform a MINUS operation, the two bindings for ?value are not seen as the same.