I was able to identify a half dozen bad nodes which when blocked cause virtually all of the errors to stop. I don't want to post IP addresses, but if you are having trouble with your log file getting too big and you are able to block IPs in a firewall, PM me and I'll send you the list.
Most errors now come from three IP addresses.
Two of them belong to Minergate and the other to some russian private pool.
Minergate is mining on his own invalid chain as you can see on their block explorer.