Not sure why, but it seems CloudFlare is blocking the bingbot. I got this message today. I don’t see any problems with the rate limit, but I do see the firewall blocking what it seems to think are fake bing bots - Rule message Anomaly:Header:User-Agent - Fake Bing or MSN Bot
We encountered a large number of requests that returned the following status: 403 (Forbidden) .
We saw 1206 errors of this type, which accounts for 15 percent of all requests we made during the last 24 hours.
Your server is denying access to your pages to Bingbot.
Check if you are unintentionally blocking some or all Bingbot requests on your server.
To see which pages were affected check Crawl Information. Note that we were able to send this message before uploading the full crawl data to your Webmaster Account so there may be a delay. Learn more.
The Bing Webmaster Team