When Installing the latest draytek firmware on a 2860, the recommended firmware is not always the best or most appropriate firmware. For example, on some circuits installing the Vectoring firmware which apparently works fine with non vectoring lines will cause the router to reboot every 30 seconds or so which gives you no possible remote remedy and requires a site visit to solve. 

30 seconds isn't enough time to flash a new image, but disabling the WAN1 interface can be done in the 30s and when that's done the router will remain up for long enough to flash the Non-Vector version. 

The moral here, is if you don't have a vectoring service, DO NOT install the vectoring firmware.