The dhcpd subnet thing is normal since eth1 is your wan interface. You don't need to provide DHCP addresses over the WAN, that's the ISP's job.
These logs occur during boot:
Sep 21 06:50:02 ubnt ubnt-service-ssh: starting the SSH service (see messages from sshd). Sep 21 06:50:02 ubnt ubnt-service-gui: starting the GUI service. Sep 21 06:50:21 ubnt ssh-recovery[683]: terminating the SSH recovery service :: pid=(611)
Looks like it rebooted to me. Unexpected reboots can be power problems, also crash related. Hard to pin down without some additional remote logging.
You should be able to see the uptime using this command to verify it rebooted:
show version
Is the unit on a UPS?