I can confirm that I am seeing this bug on some of our 2960-X series switches that have recently been upgraded to 15.2(6)E1. The log messages I see are slightly different but we do have DHCP Snooping enabled on all our switches:
%SISF-3-INTERNAL: Internal error, Invalid event State :MAC-REACHABLE, Event :MAC_VERIFIED -Process= "SISF Main Thread", ipl= 0, pid= 448
-Traceback=: 80E6DCz 1CD6E98z 1C84DA4z 1C69508z 1C865ACz 1C871C4z 1CAEC0Cz 1CD8B8Cz 3BC696Cz 3BCA6ACz 1CD8F5Cz 3B30F98z 3B1DE5Cz 3B19B4Cz
The 5 minute CPU on these switches was sitting at 69%. Turning off DHCP Snooping is not an option for us so I applied the ipv6 filter workaround to the uplink ports only (I reasoned only ports that have 'ip dhcp snooping trust' configured) -after applying the workaround the 5 minute CPU dropped to a more respectable 40-43%.
