Watch Face, Background makeWebRequest

Hi,

I have faced with very unexpected behavior when I'm making a web request from a temporal event.
I thought it is a system limitation, that it is impossible to invoke a background delegate frequent than once in 5 min.
But it turns out that on some devices it happens every second or even a bit faster. Simulator and my own device (F5 plus) behave totally fine but in a very rare case, on my users' devices onTemporalEvent() method is invoked as a machinegun.

The background initialization method pretty standard, just as in documentation:

 function InitBackgroundEvents()
 { 
    var FIVE_MINUTES = new Toybox.Time.Duration(5 * 60);
    var lastTime = Background.getLastTemporalEventTime();
    if (lastTime != null) 
    {
        var nextTime = lastTime.add(FIVE_MINUTES);
        Background.registerForTemporalEvent(nextTime);
    } 
    else 
    {
        Background.registerForTemporalEvent(Time.now());
    }
 }

And InitBackgroundEvents() being called from two methods:
function getInitialView()
function onSettingChanged()

So, the question. How does it happen that only on a small number of devices temporal event being invoked once in a second and how to avoid this?
Does anybody have the same experience?