Hi there,
I’m checking your LB logs, and it seems to me that the frequency in which it goes from healthy to critical is too high. If the origin is healthy and Cloudflare reports it as critical with that error, means it’s likely receiving a 524, or that your origin is taking longer than the 5 seconds you have set at your monitor.
To solve this I would start by making sure Cloudflare IP addresses are not being rate limited at your origin, you can check your origin logs.
Cloudflare IPS: IP Ranges
If this is not the issue, I would increase the timeout to 10 seconds, or create simple page to point my monitor to. For instance, if you have a simple page called monitor.html with nothing on it or only a simple text, it will load faster that your current root where you have your monitor pointing to, so it’s less likely to timeout even with 5 seconds. I would also consider spacing out the monitor interval as a tighter interval may cause load on your origin by itself.
These are my suggested settings:
Take care.