Start with a detailed listing of the hardware, OS version and what the pool layouts were. How and why did you get to this point? We can only go off what you post to the forum to try to diag.
Browse some other threads and do the Tutorial by the Bot to get your forum trust level up and post images and links
TrueNAS-Bot
Type this in a new reply and send to bring up the tutorial, if you haven’t done it already. @TrueNAS-Bot start tutorial
Why were you loading the System Configuration in the GUI? Did your boot-pool die and you were reloading your OS, etc. You have to provide enough information so we can even begin to try to help.
Wild guess is to put the 512GB drive back as the boot drive and try booting. Another option is to do a fresh install, don’t load the System Configuration and then diagnose your entire system from there.