Nighthawk app not remembering names on my R6400 router

I am using the Nighthawk app on my phone to manage my R6400 router. Firmware is up to date. I am having a problem where some device names are not remembered when I enter them. Other devices are identified even without me putting in a name. But some just show up as a generic "unknown". Sometimes when I enter a name it saves for a day or even weeks, but eventually the names disappear and it reverts back to "unknown". I then have to go to individual devices and look at the IP address in order to rename them. Very frustrating.

The desktop computer and Samsung device listed on the attached photo are names that I did not even write. They were automatically populated. Most devices automatically populate to the name "unknown."

You see I have a Chromebook identified. I'm sure at least one of the other unknowns is another Chromebook that I once identified but now it's gone. I know for sure another device is a TV that I named just last night, and it's already gone.