The office advertises 220.127.116.11/24 via BGP to both ulsfo and Zayo, and uses 18.104.22.168/28 (which is a subset of the /24) as interconnect subnet between the DC and the office.
The office NAT is 22.214.171.124.
So when the DC link went down, traffic from the Office to the DC properly went through the Zayo DIA link. But even though the office's 126.96.36.199/24 was only reachable from the DC via the Internet, that /28 exists as directly connected interface/subnet. Which cause the return traffic to any IP in the subnet to be blackholed.
This also explains why my tests to voip.corp.wikimedia.org worked fine (as it's outside that /28).
Cleanest fix is to renumber that interconnect link to use a subnet outside of the office advertised /24.
ulsfo IP space has free IPs we can use, I picked 188.8.131.52/29. see DNS CR bellow.