I have a Galaxy Note 5 running Android 7. I switched from Verizon. I have noticed that since I switched, occasionally calls go straight to Voicemail and I have no idea it happened until I receive the Voicemail alert, usually immediately after the voicemail has been left.
This seems to happen most when Wi-Fi is enabled. I even have reproduced the problem myself by trying to call my number from my wife's phone to have it go straight to voicemail, despite my phone showing full 4G reception.
Here's the catch, I disable the Wi-Fi and then try again, the call comes through.
Re-enable the Wi-Fi and try again, call goes through.
I'm not sure what's going on but it is as if the phone drops off the network but hasn't. This might explain why suddenly I receive a bunch of notification all at the same time.
It would be great if
a) someone could help identify the problem
b) there is some way to see the connectivity status of my device on the network, so I can identify when it has dropped off (and therefore become uncontactable).