Fallout 4 Pip-Boy Android app stopped connecting to PC version running on Windows 10
Solution 1:
For me this wasn't a networking issue. It was the permanent modification I had made to my carry weight that the application didn't like.
You can check by starting a new game. You have to run through until you exit Vault 111 and pick up the Pip Boy, but I wager the application will work for you for that game at that time.