16.10 appears to have a bug in the BGP routing. Routes are no longer being passed from a one-armed concentrator to a remote MX running 16.10.
We have a HA pair in our datacenter operating as a one-armed concentrator for our SD-WAN sites. The MX pair is directly connected and BGP peered to a pair of 93240's. The MX and 93240's advertise routes between each other so the two sides of the network are aware of what networks exists on the other side.
Upgrading a test site to 16.10 has made it clear that the BGP routes are no longer propagating from the MX concentrator pair to the remote MX.
I am working with support to see if they can determine the cause, but if you are doing any BGP route advertisement in to your Meraki infrastructure I would be very cautious of MX16.10.