Hi Ghochi,
I had a similar issue with Fiori launchpad configuration and fixed it by re checking the front end services (Pagebuilder, Interop , ...)to point to the front end system , rather than the Back end system. Make sure the system alias is configured properly
Did you find any error logs in the gateway ?
Also i strongly recommend to follow the suggestions mentioned by Masa at SAP Fiori - SAP Fiori launchpad troubleshooting .
Regards
Virinchy