Hi,
Other than the MTU,
SeqNumberMismatch as per RFC (section 10.3) says:
https://tools.ietf.org/html/rfc2328#section-10.3
A Database Description packet has been received that either
a) has an unexpected DD sequence number,
b) unexpectedly has the Init bit set or
c) has an Options field differing from the last Options field received in a Database Description packet.
Any of these conditions indicate that some error has occurred during adjacency establishment.
Could you check if there is any packet loss on link (unidirectional pkt loss) which could could attribute to loss of frame resulting is different DD Seq packet from neighbor.