Thanks Levo although checking something with my internet provider is rarely possible. Customer support knows nothing. But I was able to solve it. Somewhere under QOS my upload speed was 10 Mbps...

If I connect my laptop to the ISP router with a LAN cable, and do a speedtest online, I get near 40 Mbps upload speed. If I connect the same LAN cable to the main Deco instead of directly to the...