Note the request/attempt counts that page provides...
Count of 8 to 13 on the times I've been labelled a DOS attempt.
Refresh the page and the count changes.
As I'm asking for a single refresh, something else is going on.
This seems to be connected with slower response from the server, which may have your browser (or any link in the internet chain from you to the Nest server) reask for the page. Although I've been labelled a DOS attempt even when there appears to be fast server response. Add in browser pre-fetch and I suspect that the server's threshold for a DOS is a little too demanding, resulting in false positives detection of DOS.
Only happens when I'm trying to log in, with or without having already successfully viewed the forum as a guest.
Clears up on it's own, good to go the next day.