I tried to load https://openmqttgateway.com but that failed. It looks to be on a different server 213.186.33.5 . Because TLS does not work there, hsts preload is not possible: HSTS Preload List Submission
The https://community.openmqttgateway.com that is running on 51.77.156.72 at OVH hoster does not have IPv6 enabled.
Could you also enable DNS CAA? OVH supports it: Who Supports CAA Records?