Third Party Mirror-Networking Port Forwarding (Remote Connection)

Hello, I'm struggling to nail down the problem why it is not possible (anymore) to connect to my application over the internet (it worked in the past but i haven't tested this for a few months).

I'm testing with the example chat scene from Mirror. I've set the port in the NetworkManager to 7130 and opened the same port on my router according these instructions: https://www.edpnet.be/en/support/in...o-set-up-a-port-forwarding-on-a-fritzbox.html (I have a Fritz!Box 7412 but it looks basically the same).

I've set the Protocol to UDP and Port to device, through port and Port requested externally to 7130.

I'm using a Windows 10 system and have no anti virus installed other than Windows Defender. In the advanced firewall settings I've added an Incoming Rule for Mirror-Example.exe (the application I've build with unity) for All protocols on All local- and remoteports.

When I run the application, start a server and check with netstat -a I can see that there is indeed listened on port 7130 for ipv4 and ipv6 addresses on my local machine (if I interpreted those outputs correctly):
UDP 0.0.0.0:7130 *:*
UDP [::]:7130 *:*

I've first conducted following tests:
- Start another instance of the app on my machine and connect to the server with the address localhost
-> works

- Again, in another instance, connect to the server but this time with my global ipv4 address (found after a quick "what is my ip" search)
-> does not work (KCP: Connection timed out after not receiving any message for 10000ms. Disconnecting.)

- Now if I connect with my global ipv6 address
-> appearently works

It's interesting that I was not able to connect using my ipv4 address (I could have sworn it worked before), but this is not my biggest concern atm.

To test a remote connection I've send a copy of the application to some friends (along both my ipv4 and ipv6 addresses) and asked them to try to connect to my server. Neither of them was able to.

So I am currently at a loss, i have no idea what else could block the connection, especially since it worked without issues a few months ago (I haven't updated anything (relevant to this issue) myself, as far as I can tell).

Since I cannot always rely on a friend helping me out to test this with me I occassionally check with a Port Scanner (like http://www.ipv6scanner.com/cgi-bin/main.py) if the opened port is actually recognized while the server is running. Depending on the tool I check with I get either the result Filtered or Blocked. Though I have no idea if this is a reliable test, I would appreciate it if someone could clarify.

Other things I've tried (with same results):
- Adding an Outgoing Rule for the application (not sure if that is needed though)
- Disabling the firewall completely

 

same here please help!