Add logging & possible fix for #96618 (#96619)

Suspect this test needs merges to be disabled, but in case it's not that
then this commit also makes the logging more verbose.

x-pack/plugin/snapshot-based-recoveries/src/internalClusterTest/java/org/elasticsearch/xpack/snapshotbasedrecoveries/recovery/SnapshotBasedIndexRecoveryIT.java

@@ -66,6 +66,7 @@ import org.elasticsearch.snapshots.SnapshotInfo;
 import org.elasticsearch.test.ESIntegTestCase;
 import org.elasticsearch.test.InternalSettingsPlugin;
 import org.elasticsearch.test.MockLogAppender;
+import org.elasticsearch.test.junit.annotations.TestIssueLogging;
 import org.elasticsearch.test.junit.annotations.TestLogging;
 import org.elasticsearch.test.transport.MockTransportService;
 import org.elasticsearch.threadpool.ThreadPool;
@@ -664,6 +665,10 @@ public class SnapshotBasedIndexRecoveryIT extends AbstractSnapshotIntegTestCase
         }
     }
 
+    @TestIssueLogging(
+        issueUrl = "https://github.com/elastic/elasticsearch/issues/96618",
+        value = "org.elasticsearch.indices.recovery:TRACE,org.elasticsearch.xpack.snapshotbasedrecoveries:TRACE"
+    )
     public void testCancelledRecoveryAbortsDownloadPromptly() throws Exception {
         updateSetting(INDICES_RECOVERY_MAX_CONCURRENT_SNAPSHOT_FILE_DOWNLOADS.getKey(), "1");
 
@@ -673,7 +678,11 @@ public class SnapshotBasedIndexRecoveryIT extends AbstractSnapshotIntegTestCase
             String indexName = randomAlphaOfLength(10).toLowerCase(Locale.ROOT);
             createIndex(
                 indexName,
-                Settings.builder().put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1).put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0).build()
+                Settings.builder()
+                    .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
+                    .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
+                    .put(MergePolicyConfig.INDEX_MERGE_ENABLED, false) // merging might change the primary segments after the snapshot
+                    .build()
             );
             ensureGreen(indexName);