Have you ever experienced networks that block cloudflare?

I was at a meetup event not long ago and noticed that my cloudflare zero trust was not working on their network.

Just wondering why that would be or if I am just imagining things.

Possibly from hackers using it? Or possibly in an education environment for learning security?

On a shared network (guest WiFi) the general intent is to protect the network you are connected to. They may have their own DNS filtering, in which case blocking your bespoke filters are within their remit. I carry a tethering device or 3 where I control access when those policies interact negatively with my own defaults.