No, the obi doesn't have a static address, I never had a problem with this, but I'll give it a static address to see if it makes any difference. Btw, my understanding is reboot due to this should have reason code 12 or 13, but I am getting code 6.
I have not changed the settings of the obi for a while and it's been up for over 20 days before it started rebooting daily starting a couple days ago.

Does your OBi Device have a static IP Address? If not, set a Static IP. Those are the only two things I can think of that would cause a reboot every 24-hours. Others have stated that a mis-configured Digitmap/Inbound/Outbound Call Route can cause reboot issues. Have you made any changes to your ATA recently?