Flutter: GroupedListView not working as it should

Why are my first date and first 2 items correctly built but not the rest? The first date header wrap my text correctly but the padding is incorrect and the rest has the correct padding but does not wrap my text. This is how it looks like right now.

GroupedListView<dynamic, String>(
                    shrinkWrap: true,
                    elements: activityList,
                    groupBy: (element) => element['date'].substring(0, 10),
                    groupSeparatorBuilder: (String groupByValue) => 
                      child: Container(
                          height: 35,
                          width: 125,
                          decoration: BoxDecoration(
                            shape: BoxShape.rectangle,
                            borderRadius: BorderRadius.circular(25),
                            color: themeProvider.isDarkMode
                                ? Color(0xFF64B6F7)
                                : Color(0xFFFFCC00),
                          ),
                          child: Center(child: Text(...))
                    ),
                    itemComparator: (item1, item2) =>
                        item1['date'].compareTo(item2['date']),
                    itemBuilder: (context, element) { 
                      return Card(
                        elevation: 5,
                        margin: EdgeInsets.symmetric(vertical: 15),
                      child: ListTile(
                        //listtile
                      ),
                    );},
                    useStickyGroupSeparators: true,
                    floatingHeader: true,
                  )

The problem is caused by useStickyGroupSeparators but I would want to use that.

Based on your code, I tried to reproduce the effect. Is this what you want to achieve?

The code:

class TestPage extends StatelessWidget {
  const TestPage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: GroupedListView<dynamic, String>(
          shrinkWrap: true,
          elements: items,
          groupBy: (element) => element['date'].substring(0, 10),
          groupSeparatorBuilder: (String groupByValue) => Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Container(
                  height: 35,
                  width: 125,
                  decoration: BoxDecoration(
                    shape: BoxShape.rectangle,
                    borderRadius: BorderRadius.circular(25),
                    color: const Color(0xFFFFCC00),
                  ),
                  child: Center(child: Text(groupByValue))),
            ],
          ),
          itemComparator: (item1, item2) =>
              item1['date'].compareTo(item2['date']),
          itemBuilder: (context, element) {
            return Card(
              elevation: 5,
              margin: const EdgeInsets.symmetric(vertical: 15),
              child: ListTile(
                title: Text(element['activity']),
              ),
            );
          },
          useStickyGroupSeparators: true,
          floatingHeader: true,
        ),
      ),
    );
  }
}

Mock data:

final items = [
  {"date": "2022-07-08", "activity": "Activity 1"},
  {"date": "2022-07-08", "activity": "Activity 2"},
  {"date": "2022-07-09", "activity": "Activity 3"},
  {"date": "2022-07-09", "activity": "Activity 4"},
  {"date": "2022-07-10", "activity": "Activity 5"},
  {"date": "2022-07-11", "activity": "Activity 6"},
  {"date": "2022-07-11", "activity": "Activity 7"},
  {"date": "2022-07-11", "activity": "Activity 8"},
  {"date": "2022-07-11", "activity": "Activity 10"},
  {"date": "2022-07-11", "activity": "Activity 11"},
  {"date": "2022-07-11", "activity": "Activity 12"},
  {"date": "2022-07-11", "activity": "Activity 13"},
  {"date": "2022-07-11", "activity": "Activity 14"},
  {"date": "2022-07-11", "activity": "Activity 15"},
  {"date": "2022-07-12", "activity": "Activity 9"},
];