Didn't see where the switch was changed, but if that's the case, especially given it's a managed switch, there can be issues introduced by your cable modem from seeing traffic the switch is sending and treating its MAC as the device authorized to use the Internet. I had a cable modem that'd see STP, LACP, CDP or similar traffic from a directly-connected managed switch and pick that MAC as the one it'd let out. Even if the switch wasn't changed, it could just happen to have hit that circumstance by chance where it didn't before.