Xbox Nat type can't be retrieved?

Since yesterday I can no longer use the Partychat on my Xbox one S. I did some research and found out that it has something to do with my Nat guy. However, if I look at the Xbox which is my Nat type, it says: Nat type can't be retrieved.

Your NAT type should be open so that you can use Xbox Live Service without any problems.

Try it as follows, so maybe you can solve your problem:
Setup -> Network -> Xbox Live Connection Testing or Multiplayer testing