Fix ClusterReindexingService infinite loop

ee/app/services/elastic/cluster_reindexing_service.rb

@@ -100,6 +100,10 @@ module Elastic
       end
 
       true
+    rescue Elasticsearch::Transport::Transport::Error
+      abort_reindexing!("Couldn't load task status")
+
+      false
     end
 
     def compare_documents_count

ee/changelogs/unreleased/257838-fix-cluster-reindexing-service.yml

+---
+title: Fix Global Search Reindexing when reindexing task is not found
+merge_request: 46224
+author:
+type: fixed

ee/spec/services/elastic/cluster_reindexing_service_spec.rb

@@ -71,6 +71,13 @@ RSpec.describe Elastic::ClusterReindexingService, :elastic do
         expect { subject.execute }.to change { task.reload.state }.from('reindexing').to('failure')
         expect(task.reload.error_message).to match(/has failed with/)
       end
+
+      it 'errors if task is not found' do
+        allow(Gitlab::Elastic::Helper.default).to receive(:task_status).and_raise(Elasticsearch::Transport::Transport::Errors::NotFound)
+
+        expect { subject.execute }.to change { task.reload.state }.from('reindexing').to('failure')
+        expect(task.reload.error_message).to match(/couldn't load task status/i)
+      end
     end
 
     context 'task finishes correctly' do