How could this routing loop occur?

Good afternoon,

I was wondering if someone here could provide an insight into a situation I experienced today.

One of the offices I look after had a brief power cut today. When the power returned the internet connection remained down. I did a bit of troubleshooting and I saw my pings to the ISP router were expiring in transit. I ran a tracert to the ISP router IP address and noticed their seems to be a looping root.

The first 7 or 8 hops were fine and then from the 9th hop onwards it bounced between 2 IP addresses until the packet died. The below is an example of the ninth hop onwards.

8.8.8.8 8.8.8.9 8.8.8.8 8.8.8.9 8.8.8.8 8.8.8.9 8.8.8.8 8.8.8.9

I was curious as to how would the power outage cause a loop to occur? I don't know how the routers where the loop is occurring are configured as I don't have access to them. Would someone be able to explain what kind of configuration would cause this please?