Seems Tesla has changed how sleep mode works with 8.1. I am on 17.14.35 and have found my car taking naps during the day on the last couple of days where my car was parked all day. Since James has not mentioned any changes in TeslaFi, other then the work around for the missing battery current value, my conclusion is something has changed in either the Tesla software in the car or Tesla's servers.
For the record I do not have TeslaFi sleep mode enabled during the day, although I do have night time sleep and deep sleep enabled for my home location. Prior to 17.14.35, my car might stay asleep during the morning, continuing its night time sleep. But once the car woke up for the day, it stayed awake until the scheduled evening sleep period. I do have power saving selected and always connected unselected.
Looking back, this behavior seems consistent since installing 17.14.35 about 10 days ago. The car takes naps during the day, even if it wakes up for a bit before going back to sleep. (Raw data shows state of online followed by asleep.) So far, I only see the naps if before the car has been driven on a particular day. Once I've driven the car on a given day, it no longer takes naps that day.