Fly from Portland wrote on Jul 11^th, 2016 at 9:44pm:

Been using the speedbrake on descent when drag required. It has NOT been consistent in showing in EICAS. First time it is fine and alert goes off, next no message no alert, then it starts working again. Anybody else seeing this.  :-?

I have not seen this. I hope you realize  that the message comes NOT when you SET the speedbrake, but only when the speedbrake IS set AND the AP has to apply THRUST to hold the commanded speed (at level-off for example).  :)
Guy