What causes "Checkpoint '#{@checkpoint_label}' not found" in instructure/canvas-lms?

Verify @checkpoint_label exactly matches an existing sub_assignment_tag: assignment.sub_assignments.pluck(:sub_assignment_tag).

instructure/canvas-lms · error · Checkpoints::CheckpointNotFoundError

Checkpoint '# ' not found

Error message

Checkpoint '#{@checkpoint_label}' not found

What it means

DiscussionCheckpointUpdaterService#find_checkpoint looks up a sub-assignment by sub_assignment_tag matching @checkpoint_label (e.g. 'reply_to_topic' or 'reply_to_entry') and raises CheckpointNotFoundError if none exists. The updater can only modify checkpoints that actually exist on the parent assignment.

Solutions

Verify @checkpoint_label exactly matches an existing sub_assignment_tag: assignment.sub_assignments.pluck(:sub_assignment_tag).
Create the checkpoint first (creator service) before updating it.
Trim/canonicalize the tag at the API boundary to avoid whitespace/case mismatches.

Example fix

// before
updater.call(assignment: a, checkpoint_label: 'replies', ...)
// after
updater.call(assignment: a, checkpoint_label: 'reply_to_entry', ...)

Defensive patterns

Strategy: try-catch

Validate before calling

tags = assignment.sub_assignments.pluck(:sub_assignment_tag)
raise ArgumentError, "unknown checkpoint #{label}" unless tags.include?(label)

Type guard

def checkpoint_exists?(assignment, label)
  assignment.sub_assignments.exists?(sub_assignment_tag: label)
end

Try / catch

begin
  Checkpoints::DiscussionCheckpointUpdaterService.call(assignment:, checkpoint_label: label, ...)
rescue Checkpoints::CheckpointNotFoundError => e
  render json: { error: e.message }, status: :not_found
end

Prevention

Fetch valid checkpoint labels from the assignment before building update payloads
Don't reuse update payloads across different discussions
Ensure checkpoints exist (creator ran) before issuing updates

When it happens

Trigger: Calling the updater with checkpoint_label that doesn't match any sub_assignment_tag on the assignment — misspelled tag, tag on a different assignment, or the assignment has no sub_assignments at all.

Common situations: API clients using wrong tag strings ('replies' vs 'reply_to_entry'); applying an update payload built for one discussion to another; the checkpoints having been deleted (checkpoints flag disabled) while updates keep arriving; case/whitespace differences in tags.

Understand the failure class

Background: Record Not Found Errors: "not found", RecordNotFound, and "was not found" — what they mean and how to fix them — this error's family across 28 libraries.

Related errors

AI-assisted analysis of instructure/canvas-lms@1c9f0bb801 (2026-09-15). Data as JSON: /api/errors/f98d4170fdf1db7a. Report an issue: GitHub.

Appendix: source

Thrown at app/services/checkpoints/discussion_checkpoint_updater_service.rb:40

    validate_flag_enabled
    validate_dates

    checkpoint = find_checkpoint
    compute_due_dates_and_create_submissions(checkpoint)
    checkpoint.saved_by = @saved_by
    checkpoint.updating_user = @updating_user
    checkpoint.save!
    checkpoint.saved_by = nil
    checkpoint
  end

  private

  def find_checkpoint
    @discussion_topic.update!(reply_to_entry_required_count: @replies_required) if update_required_replies?
    checkpoint = @assignment.sub_assignments.find_by(sub_assignment_tag: @checkpoint_label)

    raise Checkpoints::CheckpointNotFoundError, "Checkpoint '#{@checkpoint_label}' not found" unless checkpoint

    # Only assign attributes that have actually changed to avoid triggering
    # Master Course validation on unchanged restricted columns
    changed_attributes = checkpoint_attributes_for_update(checkpoint)
    checkpoint.assign_attributes(changed_attributes) if changed_attributes.any?

    update_overrides = override_dates.select { |override| override[:id].present? }
    new_overrides = override_dates.select { |override| override[:id].nil? }
    existing_overrides = checkpoint.assignment_overrides

    override_ids_to_delete = existing_overrides.pluck(:id) - update_overrides.pluck(:id)

    # 1. Remove overrides that are no longer present
    if override_ids_to_delete.any?
      parent_override_ids = checkpoint.assignment_overrides.where(id: override_ids_to_delete).pluck(:parent_override_id)
      checkpoint.assignment_overrides.where(id: override_ids_to_delete).destroy_all

      AssignmentOverride.where(id: parent_override_ids).destroy_all

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