Well, this might set a record for the shortest working project that I thought was 'done'. Turns out AA batteries drop in voltage when cold a lot more than I expected. After some very mild cold weather (barely below freezing), the voltage dropped enough that the ESP32 wasn't able to fully boot/connect to Wi-Fi on being woken up. Obviously there are much more elegant ways to handle it, but based on what I had on hand I decided to just double the number of AA batteries I use (yes, I realize how excessive it is using 6xAA batteries to power such a simple and small device). Size of the finished project isn't really an issue, and presumably the extra voltage should mean I can eek out every bit of juice out of the batteries now. My only real concern is whether the loss from the voltage regulator on the board will start adding up more. Time will tell...