[arch-general] Tenda Nova MW6

Good morning, i realise this is not an Arch specific topic but hope you can help me here. I just acquired a Tenda Nova MW6 Mesh Wifi system and having troubles with the 2.4 GHz band. It was fine after initial setup, but after about an hour the printer is no longer able to connect (HP OfficeJet Pro 8620). My laptop (Thinkpad X201) connects but has issues with DNS. The Tenda system connects via LAN to my ISPs router and spans its own network with new subnet mask. I can ping my router and access it's management site with the IP address from a browser but not by it's web address (speedport.ip). My ISP router is a Speedport W 724V from Deutsche Telekom. Any ideas where I need to look at? Thanks Frank