Quick update on this buggy firmware: last few days due to repairing works at home, I had to switch off the mains electricity a few times, and once back up, each time the modedm re-synced at a slower speed (after last time it dispalys a sync speed of 14,156 Kb/s)... well, actually that's what is displayed on the GUI, but in reality the sync speed is still above 79Mb/s - I checked this morning on the Zen portal and it said 79,666 Kb/s and did several online speed tests which were all above 73 Mb/s
I contacted DrayTek UK and they provided me with another beta
firmware but problem is not solved, awaiting their reply
The saga continues