Cloudflare Block Bingbot

my site was working fine last days but unfortunately today all my traffic drop from Bing
I checked through Fetch as Bingbot page in Bing webmaster tools and found an error

Status: The DNS resolution for the host of the url (or the redirected url) could not be resolved.

I checked in Google and Yandex and everything is fine, so …

I cleared all cache in cloudflare and enable development mode
and Bingbot successfully fetched my site but after 3 hours the problem comes again which is after the expired of development mode and the purge cache trick didn’t work any more

How to fix this issue?

by the way, i checked all my server configuration, httaccess file, robots.txt and all are fine

That error sure sounds like it’s due to DNS. What’s the domain?

but the site is working fine in google and yandex and normal browsing

also. i checked site header and its working fine
https://www.webconfs.com/http-header-check.php
HTTP/1.1 200 OK =>

I tried to fetch again now and another error appear
Status: Unexpected Error