Weird network issue after power outage.

I'm running into a strange issue I haven't encountered before.

Link to Image

The above image has been simplified, but what I'm running into is that, in regards to the image, the host at 10.1.255.10 cannot ping 10.2.255.10. It CAN ping 10.2.255.11.

Even stranger, 10.1.255.11 can ping 10.2.255.10.

I've checked the firewall, and the packets are showing as accepted and not being blocked.

Even more strange, running tcpdump on 10.2.255.10 shows no ICMP packets hitting it from 10.1.255.10, yet, when 10.2.255.10 pings 10.1.255.10, the host replies back, but the reply never reaches back to the 10.2.255.10 host.

Here's the kicker -- this was all working COMPLETELY fine and there were no issues at all until recent events: a Transformer exploded nearby and knocked out power to the entire building for hours. Backup batteries only lasted so long before everything sort of died down in a dirty state which I've been able to mostly recuperate from, except for this bizarre issue.

I've compared switch config backups and absolutely nothing has changed -- only the power outage, which seems to have some effed up lingering effect.

Any ideas?