We were at WDW last week; we did not do pre-registration and went to guest relations at the Epcot intl gate on the Sunday evening (28th)--which was a non park day for us--and had our
DAS set up there.
The only day where the DAS icon would NOT show up in my dad's app was this past Saturday (4th). I tried forcing it closed, logging him out/back in, but it wouldn't show up. We didn't realise this until we were at dinner, because shortly after our arrival to the park we had gone to a guest experiences umbrella to have friends added to his list, and they set a ride for us. After that initial ride we went to dinner, and it was only towards the end of dinner that we found that the app wasn't loading the DAS option. We ended up just leaving the park after dinner; had the app been working, we would have set up a ride, but we weren't going to mess with trekking to an umbrella at that point.
On one day (Thursday, I believe), the app worked from our hotel room and let us set a return time before we entered a park (this was Thu mid-day; we hadn't gone to any park yet that day). But that seemed to have been a one off glitch, albeit a beneficial one.
We did have it on one ride (Jungle Cruise) where the app thought my brother hadn't swiped in, so wouldn't let us include him in the party for setting a new time. But we just went back to the CM after the ride and they cancelled it on my brother's profile.
I do remember trying to cancel a DAS reservation one day and feeling like I was going in circles trying to find the right process, but of course I can't remember the details now.
At the deluxe extended evening hours at MK I found out that they were issuing DAS times on Mine Train--they said it just wasn't an option in the app and they had to set it at the ride. I didn't ask at other rides; only found out at this ride because I asked a CM why there were two lines--I hadn't even thought of DAS as being an option
So just a few very small hiccups, and we found it SO NICE to be able to set return times on the app.