Trouble with IoT smart plugs dropping offline every few hours

We recently bought an outdoor smart plug from POWRUI to control our lights, bird bath, etc.  After setting it up through the 2.4G network, the managing app shows that the device goes offline and back online throughout the day.  We set up a couple of TopGreener plugs a couple of years ago and have never had a problem with them.  

I've read some articles about setting up the IoT devices through their own router, or reserving their IP addresses, or setting them up in a DMZ, but we haven't been able to resolve the issue.  Has anyone else had this problem - and solved it?