Simply downgrading from 4.8.2-op24 to 4.8.0-op24 or to the stable 4.7.7 versions “without keeping settings” and operation was still quite flakey (router was even providing odd DHCP outwith the assigned subnet range!). I can however confirm that a debrick process using Uboot to 4.8.0-op24 restored order and router is running smoothly without a hitch since.