Unable to save initial setup

Hi, I’ve recently bought an ardupilot apm 2.8, I’m a beginner on that flight controler.
My issue is that if, after having set the initial setup on mission planner, and I disconnect the controler from my pc and I reconnect it, it’s like if the ardupilot was new, the horizon indicator shows a nonsense indication, as if the previous setting have been erased.

Please, can anyone help me?