Thanks @marsman, that at least confirms that the Yocto update solves the boot issue with the latest Pi 4 revision 
Hello. Funnily enough, i have the same issue now. I have to use version 3 of Gateway OS. I tried 3.5 and 3.6 from “Index of /downloads/chirpstack-gateway-os/raspberrypi/raspberrypi4/” and they are not booting. Hasn’t this been fixed everywhere?
This is quite some time ago (years), and I can’t remember when and where a fix was included. Please note that v3 is very old, and is no longer updated / maintained. For ChirpStack v4 I have switched to OpenWrt as a base. I would recommend using v4 instead when possible.