This is very strange. Seems unique to that device and the mydlink Lite app.
What version iOS are you running?
Did you upgrade iOS from 10.3.x? I have heard "upgraders" have experienced issues with apps in general.
When not a connection issue, most of the time uninstalling the app, reboot phone (regular reboot, not a force restart), and reinstall app solves these kinds of issues.
Have you contacted Tech Support (other than through mydlink.com)?