Enable Parsoid.
This not working:
[ { "aaa": "mmm", "templates": [ { "title": "test1", "elements": [ {"something": "ss"} ] } ] } ]
empty page rendered.
example: https://pl.wiktionary.org/w/index.php?title=MediaWiki:Gadget-insert-inflection-data.json&useparsoid=1
This works:
[ { "aaa": "mmm", "templates": [ { "title": "test1", "elements": [ "sss" ] } ] } ]
shows the table
example: https://pl.wiktionary.org/w/index.php?title=Modu%C5%82:statystyka/dane.json&useparsoid=1