Thanks for reporting the issue. I suspect it's related to the use of LineLink. At the moment, we're still working to get LineLink to be fully supported with DIGITS. We will have a release later in the month that allows for full support and will require our special care to upgrade your LineLink rateplan to the new plan. We will post out into the forum when it's time to upgrade and use LineLink fully with DIGITS.
For the time being, I'd suggest not to utilize LineLink in this manner as it may cause your phones not to ring.
I have turned off LineLink on my S7. I have left it active on my Tab E.
I'll add a response here after I have been able to evaluate if it makes a difference. (At least a few days.)