Assuming the fridge display represents the whole compartment is the trap—door shelves, corners, and the back can have noticeably different temperatures.
A vial in the fridge door can experience a very different temperature pattern than one on the middle shelf. That’s the most interesting part—“2–8°C” describes a range, not uniform or stable storage.
For example, are you referring to temperature variation between the back of the fridge and the door shelf? How wide is the spread you’re seeing within that 2–8°C range?
Discussion 22