Cloudflare - can't provide a secure connection

I’m using a self hosted version of discourse and have come across this issue where cloudflare SSL seems to only work with some browsers. I’ve tried asking this in cloudflare community already.

The forum can be found: https://robloxforum.net

What is the error message?

This site can’t provide a secure connection robloxforum.net 1 sent an invalid response. Try running Windows Network Diagnostics. ERR_SSL_PROTOCOL_ERROR

What is the issue you’re encountering

Cloudflare SSL isn’t providing a secure connection. I’ve tried fixing it but have no idea how. The website I’ve noticed works on google chrome but not opera gx nor Firefox.