I have now confirmed the issue, but I have also determined it does not always happen, and there is a third state where the app doesn’t communicate at all. For these tests I used my phone (instead of tablet).
First, with the phone connected to home WIFI and the app showing me a 4Hz update feed, I drove away. When the phone switched to cell data, the feed froze and did not recover on its own. In this scenario I could not tell whether app-to-device messages were also failing.
Second, with the phone connected to cell data and the app showing me a 4Hz update feed, I drove home. When the phone switched to WIFI upon arrival, the app fully reconnected and continued the feed.
Third, just for kicks, I turned the phone’s wifi off for 20 seconds, and then back on for 20 seconds. I kept doing this in 20 second increments, forcing the phone to switch to cell data, and then back to wifi. The first 2-3 times the app reconnected just fine, but then it failed and remained disconnected entirely.
Fourth, I tried to repeat the first test by just walking away from the house. The phone never did fully switch to cell data, but the wifi had a lot of disconnects that eventually disrupted the blynk app. When I walked back into strong wifi signal, the app remained silent. I confirmed that data was not flowing in either direction from my phone, but the tablet was working fine. I then let the phone “sleep”, forcing blynk into the background without killing it. When I woke up the phone, the blynk app reconnected and began partially working again; sending data, but not receiving any (just like my original post, but on a different device). I tried the blynk pushbuttons on both the the phone and the tablet. The device and the tablet both acknowledged blynk buttons pressed on the phone, but the phone did not acknowledge buttons pressed on either the tablet or the device.
So, sometimes the app goes completely offline (and stays that way), and sometimes it goes half offline (and stays that way), and sometimes it traverses these reconnects with no trouble at all. I don’t know how useful that is, but there you have it.