nRF52832 won't wakeup after shutdown (nrf_gpio_cfg_sense_set & NRF_LPCOMP)

Question

Hello, 
 
 We are building products using the nRF52832. We have customers that experience issues that the device won't turn on again after it was turned off. The device should turn on again after a button is pressed (pin sense) or an external power is connected to the device (LPCOMP) (see code snippet below). The issue can only be resolved by disconnecting the battery from the device so the MCU is doing a low power reset. So neither the pin sense nor the LPCOMP are working. Could it be that any of the peripherals are not turned off correctly or are still in any busy mode? 
 We tried very hard to reproduce this issue but we were not able. 
 
 We are using version 2.1.0 of the nRF Connect SDK. We are using the following peripherals and modules: 
 - ADC with SAADC (nrfx_saadc) 
 - PWM (nrfx_pwm) (5 PPI channels) for LED control 
 - NRFX_TIMER_INSTANCE(3) 
 - NRFX_TIMER_INSTANCE(1) (only to do some FX calculations) 
 - Shockburst (4 PPI channels), modified code to be compatible with nRF24L01+ 
 - Settings API (NVS)

int MainStateMachine::shutdown_device() {
 // Disable all peripherals
 // ...
 SystemController::shutdown();
 return 0;
}


K_WORK_DEFINE(SystemController::shutdown_work,
 SystemController::shutdown_main_thread);

void SystemController::shutdown(void) {
 k_work_submit(&shutdown_work); // -> Call from main thread
}

void SystemController::shutdown_main_thread(struct k_work *work) {
 /* Configure to generate PORT event (wakeup) on button 1 press. */
 nrf_gpio_cfg_input(BUTTON_PIN, NRF_GPIO_PIN_PULLUP);
 nrf_gpio_cfg_sense_set(BUTTON_PIN, NRF_GPIO_PIN_SENSE_LOW);

 //wake up from sleep mode if external voltage is applied
 NRF_LPCOMP->REFSEL = LPCOMP_REFSEL_REFSEL_Ref3_16Vdd;

 NRF_LPCOMP->PSEL = LPCOMP_PSEL_PSEL_AnalogInput6;
 NRF_LPCOMP->ANADETECT = 1; // UP, Generate ANADETECT on upward crossing only

 NRF_LPCOMP->ENABLE = 1;
 NRF_LPCOMP->TASKS_START = 1;

 k_msleep(10);

 nrf_power_system_off(NRF_POWER);

 // Should never be reached
} 
 
 Do you have any idea what could block a normal shutdown of the device? 
 
 Thanks in advance! 
 
 Best regards, 
 Jonas Höfer