Drycreeker, it's your battery! It is failing and the voltage is below specifications. On most modern cars, even a slight drop in voltage causes electronic modules to misbehave. You provided the crucial clue in your message: "All of these events returned to normal the next time the care was driven." Another hint: if the battery cables have any corrosion at all, I recommend you replace them with new stock Volvo ones. Car electrical problems are incredibly frustrating.