Hi Jasheer,
I have seen this before and believe this translates to the OSPF neighbor changing state from FULL to EXSTART because of the receipt of a Database Description (DBD) packet from the neighbor with an unexpected sequence number.
SeqNumberMismatch means that a DBD packet during OSPF neighborship negotiation has been received that either:
- has an unexpected DBD sequence number
- unexpectedly has the Iimit bit set
- has an Options field differing from the last Options field received in a Database Description packet.
This can be attributed to (Unidirectional) packet loss as a possible cause.
So I would take a look at the port that the neighbour is connecting through and check for any packet loss.
Thanks.