Additional interfaces do not survive a reboot before the setup wizard has been run
In a fresh install before the setup wizard has been run or dismissed the file /conf/trigger_initial_wizard exists.
Whilst that file exists if you enable additional interfaces and set IPs etc those changes will be lost at reboot.
Changes made to interfaces enabled by default, WAN and LAN usually, are retained.
It appears that something triggered by the existence of that file disables any interfaces that are not enabled in the default config.
See attached example from an XG-7100 running a clean install of 2.4.5.