More precisely, an issue with different literal types instead of one like in XML.

In XML, every attribute or text fragment is a string, to be POSSIBLY parsed as a string, integer, date etc. according to what applications choose to do (usually according to an explicit schema).

In JSON, YAML, etc. there are at least integers, strings and floating point numbers, introducing arbitrary representation choices (1, 1.0, "1", "1.0") and implementation artifacts (e.g. numerical limits).