Problem with a timer counter.

I set a timer to count 500us ticks

TIM_InitStruct.Prescaler = (uint16_t)40000-1; //SYSCLK = 80Mhz – 80Mhz/40000 = 500us
TIM_InitStruct.CounterMode = LL_TIM_COUNTERMODE_UP;
TIM_InitStruct.Autoreload = 0xFFFFFFFF; //TIM2 – 32-bit counter
TIM_InitStruct.ClockDivision = LL_TIM_CLOCKDIVISION_DIV1;
TIM_InitStruct.RepetitionCounter = (uint8_t)0x00;
 
LL_TIM_Init(TIM2, &TIM_InitStruct);

I get the counter in milliseconds

uint32_t TIM_GetTimeStamp_ms(TIM_TypeDef * TIMx)
{
 //timer 32-bit
 volatile uint32_t time_stamp = TIMx->CNT; 
 
 //conter counts in 500us ticks so - us/2 = ms
 timer_counter = time_stamp >> 1; 
 
 //global
 return timer_counter;
}

I test it

while (1)
{
 ts1 = TIM_GetTimeStamp_ms(TIM2);
 Delay_ms(100);
 ts2 = TIM_GetTimeStamp_ms(TIM2); 
 
 time_stamp = ts2 - ts1;
}

And I see time_stamp = 100 – so far so good.

Now I test it this way

while (1)
{
 ts1 = TIM_GetTimeStamp_ms(TIM2);
 
 if (ts1 >= script_cycle)
 {
 time_stamp = ts1 - script_cycle;
 script_cycle = ts1 + 100;
 }
}

And I see time_stamp is growing up. Do I miss something?