"Are you talking about the Engine Start/Stop when driving function and stopped at a light or stop sign?"
Yes, this is what i'm referring to. I don't believe any of the conditions you mention apply here. It is an SEL, it is not in sport mode. I have observed the condition where Engine Start/Stop doesn't work when the engine is not warmed up, and I don't think it's that. This is new behavior in the last week or so. I have not turned Engine Start/Stop off either with the steering wheel control or the center console switch. I haven't done a longer drive this week to test it, but I will soon but before this started happening, my daily commute was long enough to make the feature perform as designed, so this lack of function now has me somewhat concerned. I also saw this:
The system may not shut down the engine under certain conditions, for example:
To maintain the interior climate.
Low battery voltage.
The outside temperature is too low or too high.
The driver's door has been opened.
Low engine operating temperature.
Low brake system vacuum.
If a road speed of 5 km/h (3 mph) has not been exceeded.
The driver's seat belt has not been fastened.
With regards to the rear defrost, I have been using remote start. I'll start it manually from inside the car and see what happens then.