You're seeing this on the app right?
I don't think this is a bug but rather more of a feature.
The Spark EVs battery will never be fully empty and at the same time it will never really be fully charged since there are always some little sensors drawing current like the sensor that knows when you press the unlock key.
So even if you charge the car for a week and the green light turns flashing, as soon as you unlock the car and watch the lights flash you can see that some electricity has been used.
So basically the Spark's computer will say fully charged when you get near the capacity For you it seems like +/-5%
For example, let's say I wake up with a "fully charged" car (car will not charge any more if plugged in), I unplug it and drive it down the end of the block using less than a mile on the dash. If I park it and check the app in an hour it will stay say fully charged, but if I were to plug it in it would probably still charge, even if only for a few minutes.
So there is essentially a range of capacity where the app will read as fully charged and you have all the battery cells green on the dash.
That said, even if it says fully charged, there could still be some capacity left and it will continue charging.
I would only alert the dealer if your Spark stops charging at 94%. It should keep charging from 94% to 100% and say fully charged the whole time. Next time it happens go outside and check the light to see if it's charging or not.