Constant (?) ping failures - internal_error

Hello, I have problems with pinging some of my websites.

I set up website url to monitor, and a substring required in response for a valid result.
The website has SSL and is behind Cloudflare.

Monitor reports downtime nearly all the time. What is confusing me it is not all the time, sometimes monitor marks website as working. From my observations- mostly when I change monitor settings.
What can I do to fix this issue?

Permalink to example event:

Hi @pp_1 pp_1 - This may be related to the legacy availability monitor. We have seen false pings with it before and are encouraging users to move to Synthetics monitoring.

However, this may also be due to your firewall. You can whitelist the Availability Monitor IP Address, if you would like to continue using the legacy monitor.

If you would like to move to Synthetics, here are a few docs to help you, as well as the list of IPs for the Synthetic minions.

Please let us know if you have any questions.