ngx-bootstrap modal after update to 11 my backdropRef is undefined

Question

I have the canDeactivate function, and when the data is not saved, I call the modal window,

public canDeactivate(nextState?: RouterStateSnapshot): boolean {
if (this.formChangeUnsaved) {
  this.bsModalRef = this.modalService.show(ModalConfirmFormUnsavedComponent, {
    backdrop: true,
    ignoreBackdropClick: true,
    keyboard: true,      
  });

  this.bsModalRef.content.confirm.subscribe((isSaved) => {
    if (isSaved) {
      this.clientApi.autoSaveFormNextStateUrl.next(nextState.url);
      this.bsModalRef.hide();
    } else {
      this.bsModalRef.hide();
      this.formChangeUnsaved = false;

      void this.router.navigateByUrl(nextState.url);
    }
  });
  return false;
}

return true;

}` }

and after switching to another url I have a modal window called and at the first call everything is fine, I switch back to the component and switch to another url again to call the modal window again then my backdropRef is undefined, this appeared after the update to 11.0.2