I would presume that there was an issue between Draytrek and your ISP service.
Yes, I would use this DLink MODEM in bridged mode. This effectively turns off any router options and functions OFF on the MODEM, making it a stand alone modem. This will pass along to the external ROUTER any and all public addressing and traffic. The external ROUTER will then handle PPPoE or A DSL account info, all traffic, management, port forwarding, Wifi and QoS that it has. Use the external ROUTER to set up reserved IP addresses for ALL connected devices on it then set up QoS and Port Forwarding as needed.
Should look something like this:
ISP DSL Line>DSL-2704B Modem>External Router(Any Router Mfr should work)><connected PCs and Wifi devices to external router.