Cloudflare can have issues if the network connection is unstable. I think it may be that a client that is losing network packets resembles a particular type of attack. I don’t know why, but Cloudflare in Safari seems particularly sensitive.
Just a couple of days ago, I was using a wireless network that was dropping ~5% of its packets, and I could not pass the Cloudflare test while trying to access a particular shipping site I use.
The Cloudflare challenge loaded but failed repeatedly using Firefox, and it wouldn’t load at all under Safari. I switched from the wireless network to my mobile hotspot, and Safari and Firefox both connected and passed the Cloudflare challenge immediately.