Error loading website from accessible IP

Hi, I have created a couple of C# .NET 5 websites and deployed them via Kestrel to my Raspberry Pi. I am using Docker and the setup I have is:
Website1 - uses port 5000 and port 5001 (https)
Website2 - uses port 5002 and port 5003 (https)

I configured port forwarding on my router with a range from 5000 to 5050. This must be setup correctly since Website1 is accessible from outside my network just fine and external IP works fine.

I can access Website2 from any machine on my local network (using raspberrypi:5002) but if I try to access from a device not connected to my network (using external IP address) then it fails to load. I noticed this error on the Pi:

An exception was thrown while deserializing the token.
Microsoft.AspNetCore.Antiforgery.AntiforgeryValidationException: The antiforgery token could not be decrypted.
—> System.Security.Cryptography.CryptographicException: The key {b0a63215-b1e3-42f7-8d5b-921be6ed3d1a} was not found in the key ring.

It seems strange this error appears but I probably don’t understand it to be honest as I normally just write code. Can anybody please advise what the problem might be?

Ok, I have discovered that the website loads fine if I turn off the Wifi on my phone. My network seems to be ‘blocking’ the website somehow. The port I guess.