why do I want to edit a product or edit a page and open several windows tabs to open product edit, it always takes a long time to error 503 or 524 or the internet is disconnected
May I ask if you’re using some website editor/builder like WP Bakery, Elementor, etc. or? 
Before moving to Cloudflare, was your Website working over HTTPS connection?
May I ask what SSL option have you got selected under the SSL/TLS tab at Cloudflare dashboard for your domain ( Flexible, Full, Full Strict … )?
Regarding the 503 from the screenshot you’re sharing, it might be also that your web hosting is busy and not very much likely optimized to handle those PHP requests 
Furthermore, you’re seeing this at an page of the WordPress plugin which isn’t the official one from Cloudflare.
Since it’s related to the WordPress, I’d suggest you to whitelist your origin host / server / hosting IP address by navigating to the Security → WAF → Tools → IP Access Rules with the action “allow” for your Website and try again.
It knows to happen due to the WordPress using HTTP/1.0 and empty user-agent, therefore while executing WP-Cron or some other related JSON/REST API request via plugin.