You appear to have an instance of dnsmasq running, and this is preventing pi-hole.FTL from binding to port 53. Let's confirm - what is the output of this command from the P-hole host terminal:
Don't know why - it's not a service I've ever installed or used that I remember.
I did some thrashing around on my own trying to troubleshoot this so I can't be sure I can blame it on the installer... This time I just killed the process and away it went.
Regardless, it's working this morning, and survived a reboot properly, so let's call it fixed