The 2.6 client gets the version message, parses it fine until it gets to the subver string then throws errors. As a result it cannot read the block height that comes after. The substr issue is the issue we are looking into, could be due to sending serialised string as the numbers before worked.
We have found the exact line of code where 0.13 stops syncing, basically PoS hash does not meet the target. The block is Decemeber 2017. Not sure if it is a bit of a rogue block or of the issue is with the new client.Peter Will get all values for CheckStakeKernelHash from 2.6 and compare tomorrow.