Because some search engines don’t fully support the JSON-LD format, I decided to use the RDFa also.
When I check my HTML with the Google Structured Data Testing Tool in the result panes it shows me 2 NewsAricles, but actually there is only one.
Is it a good practice to use two equivalent JSON-LD and RDFa rich snippets on the same page?
It can make sense to provide the same data in different syntaxes: if one consumer only supports JSON-LD and another consumer only supports RDFa, it’s the only way to let both consumers make use of your data.
It would be useful to denote that both representations are about the same thing. You could do this by specifying the URI that represents this thing:
JSON-LD:
@id
Microdata:
itemid (the vocabulary needs to support global identifiers, which, e.g., Schema.org doesn’t yet)