maybe check under the app notifications to see if u need to check a box to allow this.
I've been having the issue since the update to 26, and had already checked the notifications. Today was the last straw so I really dove into it after my post. I tried several things. In the end, what worked was to go into the iOS settings and into the storage. Selected DMSS and offloaded the app. Waited for it to clear out the app and only the data remained (easy to spot as it went from 400 megs to about 3). Then I reinstalled the app from the same place. After that I just jumped into the app and presto blamo - it works!
I thought I'd post here in case anyone stumbles on this in the future and has a similar issue.
Switching gears and since I am here, I do have another question... an issue that I still haven't managed to figure out or solve. We have 2 devices currently installed.

The issue is that when someone rings the doorbells, whichever one it was, the incoming call on the iPhones was always DMSS, so no way to know which of the doorbells was ringing. An issue, since we only answer ADG between 0800 and 1700 hours and ARM should be answered by our warehouse. Since they were all coming in as DMSS, we were forced to answer all calls, and then call down to the warehouse to alert them when the doorbell was the one from the warehouse so they could open it. You'll say to just disable it on the devices that don't need it, but we can't because after 1700 hours, once the warehouse workers leave, we have to answer the calls between that time and 1900 hours.
Things changed some months ago and from one day to the next, all of a sudden, we started getting calls from the doorbells and they started to appear as ARM and ADG, which I was glad to finally see happen. The problem is that most times they seem to be switched. Calls from ADG sometimes appear as ARM and vice-versa.
Does anyone know a fix for this? Is there a way to get this to work properly?