diff --git a/CHANGELOG.md b/CHANGELOG.md
index b381aef44b..79b4c14e66 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,9 @@ and this project adheres to
 - Fix infinite loading when reopening workflow in collaborative editor due to
   delta updates not being merged with persisted state
   [#4164](https://github.com/OpenFn/lightning/issues/4164)
+- Fix incorrect field access and version type in checkpoint creation that would
+  crash after 500 document updates
+  [#4176](https://github.com/OpenFn/lightning/issues/4176)
 
 ## [2.15.0-pre4] - 2025-12-08
 
diff --git a/lib/lightning/collaboration/persistence_writer.ex b/lib/lightning/collaboration/persistence_writer.ex
index fb462caf65..40af51b8e7 100644
--- a/lib/lightning/collaboration/persistence_writer.ex
+++ b/lib/lightning/collaboration/persistence_writer.ex
@@ -416,12 +416,12 @@ defmodule Lightning.Collaboration.PersistenceWriter do
 
       # Apply checkpoint first if it exists
       if latest_checkpoint do
-        Yex.apply_update(temp_doc, latest_checkpoint.data)
+        Yex.apply_update(temp_doc, latest_checkpoint.state_data)
       end
 
       # Apply all updates in order
       Enum.each(updates, fn update_record ->
-        Yex.apply_update(temp_doc, update_record.data)
+        Yex.apply_update(temp_doc, update_record.state_data)
       end)
 
       # Create new checkpoint
@@ -429,7 +429,7 @@ defmodule Lightning.Collaboration.PersistenceWriter do
 
       checkpoint = %DocumentState{
         document_name: document_name,
-        version: "checkpoint",
+        version: :checkpoint,
         state_data: checkpoint_data
       }
 
diff --git a/test/lightning/collaboration/document_supervisor_test.exs b/test/lightning/collaboration/document_supervisor_test.exs
index 5c1f4757a2..1b5e881a95 100644
--- a/test/lightning/collaboration/document_supervisor_test.exs
+++ b/test/lightning/collaboration/document_supervisor_test.exs
@@ -1,7 +1,9 @@
 defmodule Lightning.Collaboration.DocumentSupervisorTest do
   use Lightning.DataCase, async: false
 
+  alias Lightning.Collaboration.DocumentState
   alias Lightning.Collaboration.DocumentSupervisor
+  alias Lightning.Collaboration.PersistenceWriter
   alias Lightning.Collaboration.Registry
 
   import Eventually
@@ -812,4 +814,165 @@ defmodule Lightning.Collaboration.DocumentSupervisorTest do
       verify_cleanup(document_name, workflow_id)
     end
   end
+
+  describe "9. Checkpoint Creation" do
+    test "creates checkpoint from persisted updates", %{workflow: workflow} do
+      document_name = "workflow:#{workflow.id}"
+
+      # Create some initial document state with Y.Doc data
+      doc = Yex.Doc.new()
+      workflow_map = Yex.Doc.get_map(doc, "workflow")
+
+      Yex.Doc.transaction(doc, "setup", fn ->
+        Yex.Map.set(workflow_map, "id", workflow.id)
+        Yex.Map.set(workflow_map, "name", "Test Workflow")
+        Yex.Map.set(workflow_map, "lock_version", 1)
+      end)
+
+      {:ok, update_data} = Yex.encode_state_as_update(doc)
+
+      # Insert as an update (not checkpoint)
+      {:ok, _} =
+        Repo.insert(%DocumentState{
+          document_name: document_name,
+          state_data: update_data,
+          version: :update
+        })
+
+      # Add a second update with additional data
+      Yex.Doc.transaction(doc, "add_concurrency", fn ->
+        Yex.Map.set(workflow_map, "concurrency", 10)
+      end)
+
+      {:ok, update_data2} = Yex.encode_state_as_update(doc)
+
+      {:ok, _} =
+        Repo.insert(%DocumentState{
+          document_name: document_name,
+          state_data: update_data2,
+          version: :update
+        })
+
+      # Start PersistenceWriter
+      {:ok, persistence_writer} =
+        PersistenceWriter.start_link(
+          document_name: document_name,
+          name: Registry.via({:persistence_writer, document_name})
+        )
+
+      # Trigger checkpoint creation by sending the message directly
+      send(persistence_writer, :create_checkpoint)
+
+      # Wait for the checkpoint to be created
+      Process.sleep(100)
+
+      # Verify checkpoint was created
+      checkpoint =
+        Repo.one(
+          from d in DocumentState,
+            where:
+              d.document_name == ^document_name and d.version == ^"checkpoint",
+            order_by: [desc: d.inserted_at],
+            limit: 1
+        )
+
+      assert checkpoint != nil, "Checkpoint should have been created"
+
+      # Verify checkpoint contains valid Y.Doc data by loading it
+      checkpoint_doc = Yex.Doc.new()
+      :ok = Yex.apply_update(checkpoint_doc, checkpoint.state_data)
+
+      checkpoint_workflow_map = Yex.Doc.get_map(checkpoint_doc, "workflow")
+
+      # Verify all data is present in checkpoint
+      assert Yex.Map.fetch!(checkpoint_workflow_map, "id") == workflow.id
+      assert Yex.Map.fetch!(checkpoint_workflow_map, "name") == "Test Workflow"
+      assert Yex.Map.fetch!(checkpoint_workflow_map, "lock_version") == 1
+      assert Yex.Map.fetch!(checkpoint_workflow_map, "concurrency") == 10
+
+      # Clean up
+      GenServer.stop(persistence_writer, :normal)
+    end
+
+    test "creates checkpoint merging existing checkpoint with updates", %{
+      workflow: workflow
+    } do
+      document_name = "workflow:#{workflow.id}"
+
+      # Create initial state
+      doc = Yex.Doc.new()
+      workflow_map = Yex.Doc.get_map(doc, "workflow")
+
+      Yex.Doc.transaction(doc, "initial", fn ->
+        Yex.Map.set(workflow_map, "id", workflow.id)
+        Yex.Map.set(workflow_map, "name", "Initial Name")
+        Yex.Map.set(workflow_map, "lock_version", 1)
+      end)
+
+      {:ok, checkpoint_data} = Yex.encode_state_as_update(doc)
+
+      # Insert as existing checkpoint
+      {:ok, _} =
+        Repo.insert(%DocumentState{
+          document_name: document_name,
+          state_data: checkpoint_data,
+          version: :checkpoint
+        })
+
+      # Create a delta update that modifies data
+      Yex.Doc.transaction(doc, "modify", fn ->
+        Yex.Map.set(workflow_map, "name", "Modified Name")
+        Yex.Map.set(workflow_map, "lock_version", 2)
+      end)
+
+      {:ok, update_data} = Yex.encode_state_as_update(doc)
+
+      # Wait a bit so inserted_at is different
+      Process.sleep(10)
+
+      {:ok, _} =
+        Repo.insert(%DocumentState{
+          document_name: document_name,
+          state_data: update_data,
+          version: :update
+        })
+
+      # Start PersistenceWriter and trigger checkpoint
+      {:ok, persistence_writer} =
+        PersistenceWriter.start_link(
+          document_name: document_name,
+          name: Registry.via({:persistence_writer, document_name})
+        )
+
+      send(persistence_writer, :create_checkpoint)
+      Process.sleep(100)
+
+      # Get the new checkpoint (should be the most recent one)
+      checkpoints =
+        Repo.all(
+          from d in DocumentState,
+            where:
+              d.document_name == ^document_name and d.version == ^"checkpoint",
+            order_by: [desc: d.inserted_at]
+        )
+
+      # Should have 2 checkpoints now
+      assert length(checkpoints) == 2
+
+      # Latest checkpoint should have merged data
+      [latest_checkpoint | _] = checkpoints
+      new_doc = Yex.Doc.new()
+      :ok = Yex.apply_update(new_doc, latest_checkpoint.state_data)
+
+      new_workflow_map = Yex.Doc.get_map(new_doc, "workflow")
+
+      # Verify merged data
+      assert Yex.Map.fetch!(new_workflow_map, "id") == workflow.id
+      assert Yex.Map.fetch!(new_workflow_map, "name") == "Modified Name"
+      assert Yex.Map.fetch!(new_workflow_map, "lock_version") == 2
+
+      # Clean up
+      GenServer.stop(persistence_writer, :normal)
+    end
+  end
 end