zephyr: k_uptime_delta returns wrong times

I like to detect button events. They are selected after different holding times for a button.

A gpio interrupt is generated at every change of the button pin state. At the interrupt handler the time difference is measured between the current and the previous interrupt. For that k_uptime_delta is used. I recognized that my measured times are at least by the factor 2 to low.

My setup is a own stm32F412 board with following config:

CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC=96000000
CONFIG_SYS_CLOCK_TICKS_PER_SEC=1000

# clock configuration
CONFIG_CLOCK_CONTROL=y

# Clock configuration for Cube Clock control driver
CONFIG_CLOCK_STM32_HSE_CLOCK=24000000
CONFIG_CLOCK_STM32_SYSCLK_SRC_PLL=y

# use HSE as PLL input
CONFIG_CLOCK_STM32_PLL_SRC_HSE=y

# the board have an external oscillator
CONFIG_CLOCK_STM32_HSE_BYPASS=n

# produce 96MHz clock at PLL output
CONFIG_CLOCK_STM32_PLL_M_DIVISOR=12
CONFIG_CLOCK_STM32_PLL_N_MULTIPLIER=96
CONFIG_CLOCK_STM32_PLL_P_DIVISOR=2
CONFIG_CLOCK_STM32_PLL_Q_DIVISOR=4

CONFIG_CLOCK_STM32_AHB_PRESCALER=2
CONFIG_CLOCK_STM32_APB1_PRESCALER=4
CONFIG_CLOCK_STM32_APB2_PRESCALER=4

Maybe I setup the config wrongly or the k_uptime_delta function is buggy. Any ideas?