STM32F7: Output stays on an undefined level when set to low

Hello together,

currently I'm facing a very strange issue:

I'm working with an STM32F777.

One GPIO of the MCU is used to enable the voltage to a sensor. This pin is initialized as

GPIO_InitStructure.Mode = LL_GPIO_MODE_OUTPUT;
GPIO_InitStructure.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
GPIO_InitStructure.Pull = LL_GPIO_PULL_UP;
GPIO_InitStructure.Speed = LL_GPIO_SPEED_FREQ_HIGH;
GPIO_InitStructure.Alternate = LL_GPIO_AF_0;

This pin is set to low level after startup, to power the sensor.

To check the stability of the device we do sone endless update tests. This tests works quite good. But after about 5-6hours it crashes.

The cause of this is, that the enable pin is not set to low level correctly. With an oscilloscope I could see, that the output voltage of the pin is 2.4V.

From logs I could see, that the pin was initialized and set to low.

Following questions comes to my mind regarding this behaviour:

• Why is the voltage only 2.4V and not one of the specified ones? (0V or 3.3V)
• When and why can this happen?

Maybe someone has an idea and can help me.

Thanks in regards!