We have a customer with an OS7100 on v4.95 that is using Fusion SIP trunks set to static IP address registration so there is no username/password needed.
When the OS7100 comes back up after a power loss or any system shut down, the SIP trunks will not automatically register. The customer has to contact us and we need to go in to SIP Carrier Options and disable, save, enable, save to get the SIP Service Available to change to Yes.

We have contacted Fusion and went over the SIP Carrier Options but they had no adjustments to recommend.
Does anyone have Fusion SIP trunks on an OS7100 that automatically register after a system outage?

Try setting Multi DNS Server in 2.1.5. I have quite a number of customers that are on SoTel (now Nuso) and they wouldn't register after any kind of power outage. After setting the Multi DNS Server I don't have to touch them after a power outage. Also set DNS in 5.2.13 and you have to put in 2 DNS servers. I use Google.

As mentioned the multi dns settings help. Also upgrading to 4.99 or 5.01 has helped me in some cases as well. I believe 4.95 had a problem with this software glitch. After upgrading to 4.99 the issue went away.