My clue is start/stop not working even when enabled.
I ran my battery down by accident testing electronics in Accessory mode for extended periods with the engine off, until nothing inside turned on, and I wasn't able to even open the liftgate. Measured the support battery below 3V (yikes), but charged it up fully with a Ctek CT5, and everything was fine. After the full charge, the start/stop began working as normal, I assumed it had been disabled since I bought the car in November, but sounds like the battery had been just at the voltage threshold of not allowing start/stop to work. Now with the full charge I had to remember to disable start/stop at every start, usually forget to until the first traffic light. Then after a few trips the start/stop no longer engaged, which meant the battery had gone below the voltage again, which was a convenient way to have start/stop disabled, but sounds like a sign that the battery is sad.
