diff --git a/spec/services/tournament_snapshot_importer_spec.rb b/spec/services/tournament_snapshot_importer_spec.rb
index 129d6f0..9668045 100644
--- a/spec/services/tournament_snapshot_importer_spec.rb
+++ b/spec/services/tournament_snapshot_importer_spec.rb
@@ -37,5 +37,166 @@ RSpec.describe TournamentSnapshotImporter do
       expect(follower.name).to eq('Newer name')
       expect(follower.sync_last_imported_snapshot_at).to eq(Time.zone.parse('2026-04-14T10:30:02Z'))
     end
+
+    it 'round-trips large leader tournament graph with mismatched ids, many groups, deciders and 64-team playoffs' do
+      create_list(:tournament, 3)
+      source = create_large_source_tournament!
+      create_list(:tournament, 5)
+      follower = create(:tournament, read_only_mode: true, sync_auth_token: 'shared-secret')
+
+      snapshot = TournamentSnapshotBuilder.build(source)
+
+      described_class.import!(tournament: follower, snapshot: snapshot)
+
+      follower.reload
+      expect(follower.id).not_to eq(source.id)
+      expect(sync_signature(follower)).to eq(sync_signature(source))
+      expect(follower.teams.count).to eq(128)
+      expect(follower.stages.where(level: -1).first.groups.count).to eq(32)
+      expect(follower.stages.where('level >= 0').sum { |stage| stage.matches.count }).to eq(63)
+      expect(follower.matches.select(&:decider?).count).to eq(source.matches.select(&:decider?).count)
+      expect(follower.teams.pluck(:sync_source_id)).to match_array(source.teams.pluck(:id))
+      expect(source.teams.pluck(:id) & follower.teams.pluck(:id)).not_to match_array(source.teams.pluck(:id))
+    end
+  end
+
+  def create_large_source_tournament!
+    tournament = create(
+      :tournament,
+      teams_count: 0,
+      name: 'Large Sync Source',
+      playoff_teams_amount: 64,
+      instant_finalists_amount: 64,
+      intermediate_round_participants_amount: 0
+    )
+
+    group_stage = Stage.create!(tournament: tournament, level: -1, state: :finished)
+    advancing_teams = []
+
+    32.times do |group_index|
+      group = Group.create!(stage: group_stage, number: group_index + 1)
+      teams = 4.times.map do |seed_index|
+        create(
+          :team,
+          tournament: tournament,
+          name: "Leader-G#{group_index + 1}-S#{seed_index + 1}"
+        )
+      end
+
+      teams[0].update!(name: "#{teams[0].name} Renamed") if group_index.zero?
+      teams[1].update!(name: "#{teams[1].name} Renamed") if group_index == 15
+
+      create_group_round_robin!(group: group, teams: teams)
+      create_group_scores!(group: group, teams: teams)
+
+      if group_index < 3
+        create_decider_match!(group: group, teams: teams.take(2), hidden_points: [8 - group_index, 4 + group_index])
+      end
+
+      advancing_teams.concat(teams.take(2))
+    end
+
+    result = AddPlayoffsToTournamentAndSave.call(tournament: tournament, teams: advancing_teams)
+    expect(result).to be_a_success
+
+    tournament.reload
+    play_some_playoff_matches!(tournament)
+    tournament.reload
+  end
+
+  def create_group_round_robin!(group:, teams:)
+    pairings = [
+      [0, 1, 2, 1],
+      [2, 3, 3, 0],
+      [0, 2, 4, 1],
+      [1, 3, 2, 0],
+      [0, 3, 5, 2],
+      [1, 2, 4, 3]
+    ]
+
+    pairings.each_with_index do |(left_index, right_index, left_points, right_points), position|
+      match = Match.create!(group: group, state: :finished, position: position, decider: false)
+      MatchScore.create!(match: match, team: teams[left_index], points: left_points, hidden_points: 0)
+      MatchScore.create!(match: match, team: teams[right_index], points: right_points, hidden_points: 0)
+    end
+  end
+
+  def create_decider_match!(group:, teams:, hidden_points:)
+    match = Match.create!(group: group, state: :finished, position: 6, decider: true)
+    MatchScore.create!(match: match, team: teams.first, points: 0, hidden_points: hidden_points.first)
+    MatchScore.create!(match: match, team: teams.second, points: 0, hidden_points: hidden_points.last)
+  end
+
+  def create_group_scores!(group:, teams:)
+    teams.each_with_index do |team, index|
+      GroupScore.create!(
+        group: group,
+        team: team,
+        group_points: 9 - index,
+        scored_points: 12 - index,
+        received_points: index,
+        position: index + 1
+      )
+    end
+  end
+
+  def play_some_playoff_matches!(tournament)
+    initial_stage = tournament.stages.where('level >= 0').max_by(&:level)
+    initial_stage.matches.sort_by(&:position).first(4).each_with_index do |match, index|
+      match.update!(state: :finished)
+      ordered_scores = match.match_scores.sort_by(&:id)
+      ordered_scores.first.update!(points: 20 + index)
+      ordered_scores.second.update!(points: index)
+      PlayoffStageService.populate_match_below(match).uniq.each(&:save!)
+    end
+  end
+
+  def sync_signature(tournament)
+    {
+      name: tournament.name,
+      public: tournament.public,
+      playoff_teams_amount: tournament.playoff_teams_amount,
+      instant_finalists_amount: tournament.instant_finalists_amount,
+      intermediate_round_participants_amount: tournament.intermediate_round_participants_amount,
+      timer_end: tournament.timer_end&.iso8601,
+      teams: tournament.teams.order(:name).map { |team| team.name },
+      stages: tournament.stages.order(level: :asc).map do |stage|
+        {
+          level: stage.level,
+          state: stage.state,
+          groups: stage.groups.order(:number).map do |group|
+            {
+              number: group.number,
+              matches: group.matches.order(:position).map { |match| match_signature(match) },
+              group_scores: group.group_scores.includes(:team).sort_by(&:position).map do |score|
+                {
+                  team_name: score.team.name,
+                  position: score.position,
+                  group_points: score.group_points,
+                  scored_points: score.scored_points,
+                  received_points: score.received_points
+                }
+              end
+            }
+          end,
+          matches: stage.matches.order(:position).map { |match| match_signature(match) }
+        }
+      end
+    }
+  end
+
+  def match_signature(match)
+    {
+      state: match.state,
+      position: match.position,
+      decider: match.decider,
+      scores: match.match_scores.includes(:team).sort_by { |score| score.team.name }.map do |score|
+        {
+          team_name: score.team.name,
+          points: score.points,
+          hidden_points: score.hidden_points
+        }
+      end
+    }
   end
 end