Inaccurate/confusing oil level readings?

On my vehicle there is a button on the dashboard that when you press, measures and reports the engine oil level. Mine has been consistently reporting "too high, reduce oil level" for several days.

However, when I dipstick the oil, the level is right in the middle of the minimum and maximum marks. I only bought this van just over a week ago, and have not topped up the oil at all. The dealer that sold it said that "all the fluid levels are correct".

The owners manual states to only check the engine oil via the dashboard when the engine is "at normal operating temperature" but does not mention what temperature this means. After idling? After a long drive? After being parked overnight?

There are no warning lights on the dashboard whatsoever, only the message to "reduce oil level" when the engine oil level check button is pressed.

Is my oil level sensor faulty? Is there usually that much difference in the oil level depending on the engine temperature?