SSL Labs finds one of the certificates into my chain as "not trusted" so declares my server certificate not trusted.
FNMT-RCM / AC RAIZ FNMT-RCM appears as self-signed because it's the CA root itself.
On the other hand, Qualys declares "SSL Labs does not maintain its own trust store; instead we use the store maintained by Mozilla." but it seems Mozilla do trust this certificate because it's present on Mozilla Firefox store:
Why SSL Labs doesn't trust this certificate?