MSPI is a tunnel identifier. It is a local counter that uniquely identifies a tunnel on the given machine. MSPI is an index to the MSA (Meta SA), which contains fields common to all SAs with the same peer, methods, and IDs. When a new IPsec tunnel is established, a new MSPI is created by it, and it gets the next free MSPI number. The MSPI counter is then increased. When an IPsec tunnel is closed, the MSPI counter is decreased.
Wrong update of MSPI reference count.