Why a button in LWC component vanishes when its running in the debug mode but the same is shown in the normal mode

<lightning-button-stateful
      variant={showButtonVariant}
      selected={isButtonDisabled}
      label-when-off="Add"
      label-when-on="Added"
      disabled={isButtonDisabled}
      title="Add account"
      onclick={handleAddClick}
      class="slds-m-left_x-small"
    ></lightning-button-stateful>

Button is working fine in the mode where debug is not enabled. But when debug mode is enabled for the user, then it is not shown.