I have a laptop that refuses to access a particular domain through its WiFi

I have a Dell XPS laptop. It connects to my WiFi network. So do all my other computers, phones and tablets.

There are some websites on one domain – organise.earth – that I can’t access from the laptop browser. I can access it fine from all the other devices on my network. I can also ping it from the laptop. If I connect to a VPN, I can access it OK, just not while connected just via WiFi. Oddly, there are some other subdomains that I can access fine!

It used to run Windows 10, and it had the problem then. Now it is running Linux Mint, and it still has the problem!

The error shown is that the sites “Took too long to respond”.

I tried telnetting to port 80, and typing a normal HTTP/1.0 request for one of the problem websites – I got the expected 301 response. I tried telnetting to port 443, and was able to connect – but I don’t know how to negotiate an https connection “by hand” (if it is even possible).

Could it be some problem with HTML versions or server certificates? How could this carry over from Windows to Linux like this?