Error after migration 2211 on methods that returns a String from OCC

[Yasbet_Alvarez]

We have this error after having migrated to version 2211, OCC methods that return a String when consumed return the following error:

JSONError: Unexpected token 'P' at 1:1Pre-pay Loads must be in POS placed by AR^

For example the following method:

@Secured({ "ROLE_CUSTOMERGROUP", "ROLE_CLIENT", "ROLE_TRUSTED_CLIENT"})
@GetMapping(value = "/{id}/notes")
@ResponseBody
@ApiBaseSiteIdParam
@Operation(operationId = "getNotes")
public String getNotes(@PathVariable @Parameter(description = "id", required = true) final String id){
    return myFacade.getNotes(id);
}

The method "myFacade.getNotes(id)" correctly returns a String:"Pre-pay Loads must be in POS placed by AR"

I also did the following test where I hardcode returning a string with extra quotes and it works perfectly:

Before the migration it worked correctly, it should be noted that the endpoints were moved from /rest to /occ although I consider that this should not be the problem.

I want to think it's a "lib" that is causing the problem but I'm not sure, does anyone have an idea of what could be happening?

Thanks for your help