Frequent "403 Forbidden" errors, must be due to Cloudflare

I have two websites on two different servers used with Cloudflare. Sometimes, meaning during certain periods between 4-12 hours, I get many (like 20-50) “Failed (403 Forbidden)” messages from my monitoring service.

The IPs of the monitoring service (ServiceUpTime) are set to “Skip” at WAF and Google Search Console confirms these “403 Forbidden” errors. These cannot be due to problems with my own servers (two servers not only one) but must be due to Cloudflare.

Does anyone know what happens in such cases and particularly how to get notices for degraded Cloudflare services, and how to report or respond to such problems?