" Looks like when using the json facet api,
SimpleFacets is not used, replaced by FacetFieldPorcessorByArrayUIF "

That is expected, I remember Yonik to stress the fact that it is a
completely different approach to faceting ( and different components and
classes are involved).

But your first case, it may be worth an investigation.
If you have the tools and you are used to it I would encourage you to
reproduce the issue and remote debug it from a Solr server.
Putting a breakpoint in the Simple Facets method you should be able to solve
the mystery ( a bug maybe ? I am very curious about it. )

Alessandro Benedetti
Search Consultant, R&D Software Engineer, Director
Sease Ltd. - www.sease.io
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