diff --git a/apps/api/plane/app/views/cycle/base.py b/apps/api/plane/app/views/cycle/base.py
index bcce69bf85f..ee88ca9d901 100644
--- a/apps/api/plane/app/views/cycle/base.py
+++ b/apps/api/plane/app/views/cycle/base.py
@@ -174,6 +174,14 @@ def get_queryset(self):
                             Q(
                                 issue_cycle__issue__issue_assignee__deleted_at__isnull=True
                             )
+                        )
+                        & Q(
+                            issue_cycle__issue__assignees__member_project__project_id=self.kwargs.get(
+                                "project_id"
+                            )
+                        )
+                        & Q(
+                            issue_cycle__issue__assignees__member_project__is_active=True
                         ),
                     ),
                     Value([], output_field=ArrayField(UUIDField())),
diff --git a/apps/api/plane/app/views/issue/base.py b/apps/api/plane/app/views/issue/base.py
index d0b4e7d5e08..ecaf41c0b2c 100644
--- a/apps/api/plane/app/views/issue/base.py
+++ b/apps/api/plane/app/views/issue/base.py
@@ -505,6 +505,7 @@ def retrieve(self, request, slug, project_id, pk=None):
                         filter=Q(
                             ~Q(assignees__id__isnull=True)
                             & Q(assignees__member_project__is_active=True)
+                            & Q(assignees__member_project__project_id=project_id)
                             & Q(issue_assignee__deleted_at__isnull=True)
                         ),
                     ),
@@ -914,6 +915,7 @@ def list(self, request, slug, project_id):
                         ~Q(assignees__id__isnull=True)
                         & Q(assignees__member_project__is_active=True)
                         & Q(issue_assignee__deleted_at__isnull=True)
+                        & Q(assignees__member_project__project_id=project_id)
                     ),
                 ),
                 Value([], output_field=ArrayField(UUIDField())),
@@ -1253,6 +1255,7 @@ def get(self, request, slug, project_identifier, issue_identifier):
                             ~Q(assignees__id__isnull=True)
                             & Q(assignees__member_project__is_active=True)
                             & Q(issue_assignee__deleted_at__isnull=True)
+                            & Q(assignees__member_project__project_id=project.id)
                         ),
                     ),
                     Value([], output_field=ArrayField(UUIDField())),
diff --git a/apps/api/plane/app/views/issue/relation.py b/apps/api/plane/app/views/issue/relation.py
index 50d319a88e7..7f7fe5ce6aa 100644
--- a/apps/api/plane/app/views/issue/relation.py
+++ b/apps/api/plane/app/views/issue/relation.py
@@ -149,6 +149,7 @@ def list(self, request, slug, project_id, issue_id):
                             ~Q(assignees__id__isnull=True)
                             & Q(assignees__member_project__is_active=True)
                             & Q(issue_assignee__deleted_at__isnull=True)
+                            & Q(assignees__member_project__project_id=project_id)
                         ),
                     ),
                     Value([], output_field=ArrayField(UUIDField())),
diff --git a/apps/api/plane/app/views/issue/sub_issue.py b/apps/api/plane/app/views/issue/sub_issue.py
index 0843a9a512b..1e85695a73e 100644
--- a/apps/api/plane/app/views/issue/sub_issue.py
+++ b/apps/api/plane/app/views/issue/sub_issue.py
@@ -83,6 +83,7 @@ def get(self, request, slug, project_id, issue_id):
                             ~Q(assignees__id__isnull=True)
                             & Q(assignees__member_project__is_active=True)
                             & Q(issue_assignee__deleted_at__isnull=True)
+                            & Q(assignees__member_project__project_id=project_id)
                         ),
                     ),
                     Value([], output_field=ArrayField(UUIDField())),
diff --git a/apps/api/plane/app/views/project/base.py b/apps/api/plane/app/views/project/base.py
index 2728bf4de44..34198413912 100644
--- a/apps/api/plane/app/views/project/base.py
+++ b/apps/api/plane/app/views/project/base.py
@@ -219,6 +219,7 @@ def retrieve(self, request, slug, pk):
             )
             .filter(archived_at__isnull=True)
             .filter(pk=pk)
+            .prefetch_related("project_projectmember")
         ).first()
 
         if project is None:
@@ -226,6 +227,18 @@ def retrieve(self, request, slug, pk):
                 {"error": "Project does not exist"}, status=status.HTTP_404_NOT_FOUND
             )
 
+        project_member_ids = ProjectMember.objects.filter(
+            project_id=pk, is_active=True
+        ).values_list("member_id", flat=True)
+
+        members_ids = set(project_member_ids)
+
+        if project.project_lead_id not in members_ids:
+            project.project_lead = None
+
+        if project.default_assignee_id not in members_ids:
+            project.default_assignee = None
+
         recent_visited_task.delay(
             slug=slug,
             project_id=pk,
diff --git a/apps/api/plane/utils/grouper.py b/apps/api/plane/utils/grouper.py
index 89e154a7f75..5a6cd94a741 100644
--- a/apps/api/plane/utils/grouper.py
+++ b/apps/api/plane/utils/grouper.py
@@ -1,7 +1,7 @@
 # Django imports
 from django.contrib.postgres.aggregates import ArrayAgg
 from django.contrib.postgres.fields import ArrayField
-from django.db.models import Q, UUIDField, Value, QuerySet
+from django.db.models import Q, UUIDField, Value, QuerySet, OuterRef
 from django.db.models.functions import Coalesce
 
 # Module imports
@@ -23,6 +23,8 @@ def issue_queryset_grouper(
     group_by: Optional[str],
     sub_group_by: Optional[str],
 ) -> QuerySet[Issue]:
+    project_id = queryset.values_list("project_id", flat=True).first()
+
     FIELD_MAPPER: Dict[str, str] = {
         "label_ids": "labels__id",
         "assignee_ids": "assignees__id",
@@ -42,7 +44,10 @@ def issue_queryset_grouper(
     annotations_map: Dict[str, Tuple[str, Q]] = {
         "assignee_ids": (
             "assignees__id",
-            ~Q(assignees__id__isnull=True) & Q(issue_assignee__deleted_at__isnull=True),
+            ~Q(assignees__id__isnull=True)
+            & Q(issue_assignee__deleted_at__isnull=True)
+            & Q(assignees__member_project__is_active=True)
+            & Q(assignees__member_project__project_id=project_id),
         ),
         "label_ids": (
             "labels__id",