Mobile Printing & Cloud Printing

Apologies if I missed a prior thread with this topic.  I searched for an hour and couldn't come up with another posting of this issue, though it's hard to believe I'm the first. 

In preparation for the disappearance of Google Cloud Printing we installed the HP Print for Chrome extension on several Chromebooks in a small business office.  The HP printers (426 and 477) immediately appeared and printing appeared to work fine. 

In the weeks following the initial setup there have been reports of those printers simply disappearing from the list of available printers when users attempt to print (Ctrl-P, etc).  I blamed user misunderstanding at first but recently witnessed it myself.  When I first tried, I was able to print to a HP Print for Chrome printer. Then 10 minutes later when I went to show the user how to do it, those printers no longer appeared on the list (Destination -> See more).  We kept trying periodically as I poked at settings but never found anything to change.  Then about 45 minutes later they were back on the list again and the page successfully printed.  Other users reported this is exactly what they have seen every couple of days in routine usage.  There are 3 such printers in the office and they all disappear and reappear together.

Any chance one of you has witnessed this same behavior and has any good guesses how to address it?

HP Chromebook: Chrome OS 86.0.4240.199
Ubiquiti network components, Chromebook connected via wifi

HP 426 printers connected via hard wired ethernet ports