The generated error was “Unable to guess how to get a Doctrine instance from the request information.”.
I haven’t checked deeper in Doctrine (I know it was coming from the DoctrineParamConverter).
Anyway, I check for FosRest possiblity to add extra format without allowing them for every route (like it was done in the first place).
I finally found a way but it then seems all request goes to the FormatListener of FosRest so I needed to add a custom rules to match all request to be sure we don’t get a 406 error from FosRest.
Should be ok now …