diff --git a/backend/app/routers/projects.py b/backend/app/routers/projects.py
index 8e8d143..b95b32b 100644
--- a/backend/app/routers/projects.py
+++ b/backend/app/routers/projects.py
@@ -600,13 +600,13 @@ async def invite_members(
             source_type="project_member",
         )
 
+    await db.flush()  # Assign IDs before commit (ORM objects expire after commit)
+    member_ids = [m.id for m in created_members]
     await db.commit()
 
     # Re-fetch with relationships
     if not created_members:
         return []
-
-    member_ids = [m.id for m in created_members]
     result = await db.execute(
         select(ProjectMember)
         .options(
@@ -876,13 +876,14 @@ async def assign_users_to_task(
                 source_type="task_assignment",
             )
 
+    await db.flush()  # Assign IDs before commit (ORM objects expire after commit)
+    assignment_ids = [a.id for a in created]
     await db.commit()
 
     if not created:
         return []
 
     # Re-fetch with user info
-    assignment_ids = [a.id for a in created]
     result = await db.execute(
         select(ProjectTaskAssignment)
         .options(selectinload(ProjectTaskAssignment.user))