After years of working, a Cisco 2960 with 2 Production VLANS stopped communicating on ONLY one of those two Production VLANS. The 2960 does have a management SVI and its gateway points to a SVI on a direclty connected 3750. Both SVI's can ping each other.
Both 2960 & 3750 are connected via a fiber trunk port - encapsulation is DOT1Q.
The working VLAN's Gateway is a SVI on the 3750 whereas the non-working VLAN's Gateway/SVI is on another 3750. Both 3750's are connected with fiber trunk ports and all 3 switches can ping each other.
Myself and my tech have both verified the routing and all looks good. I even set it up in Packet tracer and it works there.
What is a real mystery is that if I telnet into the 2960 i cannot ping any devices directly connected to it. They are in different subnets but I have other 2960s setup in other areas configured the same way and they can ping their directly attached devices without a problem.
Did I get hit with a solar flare or gremlin attack?