vertical line in Stepper widget

Why there a vertical line beside Pending text?

@override
  Widget build(BuildContext context) {
    return WillPopScope(
        onWillPop: () async {
          Navigator.pop(context, true);
          return false;
        },
        child: Scaffold(
            appBar: AppBar(title: (Text("NCR Update"))),
            body: StreamBuilder<NCRTableData>(
              stream: _ncrBloc.ncrStream,
              builder: (context, snapshot) {
                switch (snapshot.connectionState) {
                  case ConnectionState.active:
                    if (snapshot.hasData) {
                      return Stepper(
                        onStepTapped: (int index) {
                          setState(() {
                            _index = index;
                          });
                        },
                        currentStep: _index,
                        physics: ClampingScrollPhysics(),
                        controlsBuilder:
                            (BuildContext context, ControlsDetails controls) {
                          return Column(children: []);
                        },
                        steps: [
                          Step(
                              isActive: _index >= 0,
                              state: _index <= 0
                                  ? StepState.editing
                                  : StepState.complete,
                              title: const Text(
                                'Part 1 ',
                                style: TextStyle(fontSize: 13),
                              ),
                              content: Container(
                                  alignment: Alignment.centerLeft,
                                  child: Column(
                                      crossAxisAlignment:
                                          CrossAxisAlignment.start,
                                      children: [
                                        Column(
                                          crossAxisAlignment:
                                              CrossAxisAlignment.start,
                                          children: [
                                            _showInfo(),
                                          ],
                                        )
                                      ]))),
                          Step(
                              isActive: _index >= 1,
                              state: _index <= 1
                                  ? StepState.editing
                                  : StepState.complete,
                              title: Text(
                                'Part 2',
                                style: TextStyle(fontSize: 13),
                              ),
                              content: Column(
                                crossAxisAlignment: CrossAxisAlignment.start,
                                children: const [Text("Pending...")],
                              )),
                          Step(
                            content: Text("efe"),
                            isActive: _index >= 2,
                            state: _index <= 2
                                ? StepState.editing
                                : StepState.complete,
                            title: Text(
                              'Part 3',
                              style: TextStyle(fontSize: 13),
                            ),
                          ),
                          Step(
                              isActive: _index >= 3,
                              state: _index <= 3
                                  ? StepState.editing
                                  : StepState.complete,
                              title: Text("Part 4"),
                              content: Text("Pending...")),
                        ],
                      );
                    } else {
                      return Center(
                          child: SingleChildScrollView(
                              physics: AlwaysScrollableScrollPhysics(),
                              child: Column(
                                  mainAxisAlignment: MainAxisAlignment.center,
                                  children: const <Widget>[
                                    Icon(
                                      Icons.format_list_bulleted,
                                      size: 80,
                                      color: Colors.orange,
                                    ),
                                    SizedBox(
                                      height: 20,
                                    ),
                                    Text(
                                      'No item',
                                      style: TextStyle(fontSize: 18),
                                    )
                                  ])));
                    }

                  case ConnectionState.waiting:
                    return Center(
                        child: Image.asset(
                      'assets/loading.gif',
                      width: 200.0,
                      height: 200.0,
                    ));

                  default:
                    return Text("Error");
                }
              },
            )));
  }

Inside your Stepper, in Part 2, Part3 and Part4, you forgot to wrap the content by an Align widget, update your code as following and it will work as expected:

                      Step(
                      isActive: _index >= 1,
                      state: _index <= 1
                          ? StepState.editing
                          : StepState.complete,
                      title: Text(
                        'Part 2',
                        style: TextStyle(fontSize: 13),
                      ),
                      content: Align(
                        alignment: Alignment.centerLeft,
                        child: Text("Pending..."),
                      )),
                      Step(
                        isActive: _index >= 2,
                        state: _index <= 2
                            ? StepState.editing
                            : StepState.complete,
                        title: Text(
                          'Part 3',
                          style: TextStyle(fontSize: 13),
                        ),
                        content: Align(
                          alignment: Alignment.centerLeft,
                          child: Text("efe")
                        ),
                      ),
                      Step(
                        isActive: _index >= 3,
                        state: _index <= 3
                            ? StepState.editing
                            : StepState.complete,
                        title: Text("Part 4"),
                        content: Align(
                          alignment: Alignment.centerLeft,
                          child: Text("Pending...")
                        )
                      ),