Hey

If its gone blue then its into setup mode, this could simply be that its failed to update the firmware and has reset itself.   Seen it just once or twice before, not common but does happen

To fix it, in the App remove the missing Deco.  The choose ADD and re-add the missing deco as you would a new device, if its blue it should appear to add fresh.  However if you cant see it, you may need to reset it manually (button on bottom) then re-add

That should sort it for you