We have had the Vigor 2820Vn for 2 years running in a coffee shop.
Connection to Wi-Fi is via WEP and a simple password.
Broadband connection is solid.
Connection upstairs via cabled ethernet never fails.

Customers have complained continually about failed ability to connect over a long long period.
Sometimes a router re-boot has solved existing issues.

When we bought the Vigor 2820Vn we believed it was the best.

Can anyone recommend an business quality adsl modem router that is simpler to set-up than the 2820vn and more robust.
Does not have to be a Vigor router ...

I know this is an old thread, but I concur exactly with the experience of the OP. Same issue and even I thought I had the best router for my site.

I have sent an email to draytek support hoping for an answer.