Issue: Z resetting after 2 minutes idle

I just started out with an Ender 3 V2. One of the first things I did was to install Marlin. (Version 2.0.9.3)
Everything works fine, except for the Z coordinate: After powering up, I start the G28 auto homing, using a BLTouch. After homing, the Z-Axis rises to the specified height. Now after exactly two minutes, the Z-coordinate resets to 0 (while the print head is midair).

I have checked through the firmware and cannot find a reason why. The following setting may be important:
#define DISABLE_Z false

Please help.

in configuration.h uncomment this define

// Turn off the display blinking that warns about possible accuracy reduction
#define DISABLE_REDUCED_ACCURACY_WARNING