We have been seeing some errors related to the MTU 1400 setting on the tunnel interface - websites hanging (not all, but some, especially those with flash, like camera interfaces), linux workstations unable to establish ssh connection, remote desktop dropping randomly. Manually setting a lower MTU (1286 did it for the linux boxes) on the client side fixes those issues. However, its not realistic to manually set MTUs on all devices.
How should we go about a permanent fix? What is the recommended MTU setting for the DMVPN tunnel?