No clues in journalctl -u mailinabox, just normal startup and SSL provisioning stuff.
Anyway I have identified 2 folders that had bad permissions resulting in /admin not being able to function, my fix was to chmod them again
/usr/local/lib/mailinabox/vendor0664 to files, 0775 to folders/home/user-data0664 to files, 0775 to folders (before requesting for SSL certs)