A branch is dark the morning after a change window

Sunday 8 November, 07:40. You are on call. The manager of branch BR2 phones: nothing works, not the tills, not the phones, not the cameras. The branch opens at 08:00. BR2 is an ISR 4331 with one WAN link to HQ router R1 (10.0.0.1/30 at HQ, 10.0.0.2/30 at BR2) running OSPF area 0 with network type point-to-point and default timers. R1's router ID is 10.255.0.1. The branch LAN is 10.42.0.0/24. Every branch has an LTE out-of-band console server. BR2 has NTP and millisecond log timestamps.