since Amahi is a derivative based on a no-longer-supported version of Fedora, I doubt we can be of much help here. You will likely have to get in touch with the Amahi people (see their forums, community page or troubleshooting page). One thing that you could check is what happens if you remove the USB stick and boot. Maybe your server is simply configured to try and boot from USB first, harddrive second.
Caveat, the following is my personal opinion: I strongly suggest you not use this product. They are basing it on Fedora 27, a quite old and - as @FranciscoD mentioned - unsupported version of Fedora. That means that unless the Amahi devs manually backported all the security fixes that happened since into their version, the operating system they base on is insecure. I doubt that they have, it would be a tremendous amount of work for no reason, and they used to follow the Fedora release cycle for Amahi 7-11.