PWM Timer generation not working with low duty cycle

At low duty cycle (like below 5%), the timer pwm stops periodically (see the attached picture). The higher the duty cycle, the smaller the stop period. Does anyone know why this happens?

For context, I am using the STM32F072 Discovery board. I use CubeIDE to generate the code with the timer setting as below:

/* TIM3 init function */
void MX_TIM3_Init(void)
{
 TIM_MasterConfigTypeDef sMasterConfig = {0};
 TIM_OC_InitTypeDef sConfigOC = {0};
 
 htim3.Instance = TIM3;
 htim3.Init.Prescaler = 7;
 htim3.Init.CounterMode = TIM_COUNTERMODE_UP;
 htim3.Init.Period = 9999;
 htim3.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
 htim3.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
 if (HAL_TIM_PWM_Init(&htim3) != HAL_OK)
 {
 Error_Handler();
 }
 sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
 sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
 if (HAL_TIMEx_MasterConfigSynchronization(&htim3, &sMasterConfig) != HAL_OK)
 {
 Error_Handler();
 }
 sConfigOC.OCMode = TIM_OCMODE_PWM1;
 sConfigOC.Pulse = 9999;
 sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
 sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
 if (HAL_TIM_PWM_ConfigChannel(&htim3, &sConfigOC, TIM_CHANNEL_1) != HAL_OK)
 {
 Error_Handler();
 }
 HAL_TIM_MspPostInit(&htim3);
}

Then in the while loop in main, I call

while(1)
{
 htim3.Instance->CCR1 = 799;
 HAL_Delay(200);
}

Thank you.