[CI] ShuffleForcedMergePolicyTests testDiagnostics failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #6102 / rocky-9_platform-support-unix
• elasticsearch-pull-request #54240 / part-1
• elasticsearch-periodic-platform-support #6081 / ubuntu-2004_platform-support-unix

Reproduction Line:

null

Applicable branches:
9.0

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: null

Issue Reasons:

• [9.0] 3 failures in test testDiagnostics (1.9% fail rate in 156 executions)
• [9.0] 2 failures in pipeline elasticsearch-periodic-platform-support (50.0% fail rate in 4 executions)

Note:
This issue was created using new test triage automation. Please report issues or feedback to es-delivery.

[elasticsearchmachine]

This has been muted on branch main

Mute Reasons:

• [main] 4 failures in test testDiagnostics (0.6% fail rate in 697 executions)
• [main] 3 failures in step part-1 (0.9% fail rate in 318 executions)
• [main] 3 failures in pipeline elasticsearch-pull-request (0.9% fail rate in 319 executions)

Build Scans:

• elasticsearch-periodic-platform-support #6079 / debian-12_platform-support-unix
• elasticsearch-pull-request #54222 / part-1
• elasticsearch-pull-request #54216 / part-1
• elasticsearch-pull-request #53311 / part-1

[elasticsearchmachine]

Pinging @elastic/es-distributed-indexing (Team:Distributed Indexing)

[elasticsearchmachine]

This has been muted on branch 9.0

Mute Reasons:

• [9.0] 3 failures in test testDiagnostics (1.9% fail rate in 156 executions)
• [9.0] 2 failures in pipeline elasticsearch-periodic-platform-support (50.0% fail rate in 4 executions)

Build Scans:

• elasticsearch-periodic-platform-support #6102 / rocky-9_platform-support-unix
• elasticsearch-pull-request #54240 / part-1
• elasticsearch-periodic-platform-support #6081 / ubuntu-2004_platform-support-unix

[ankikuma]

The following assert is firing inside ShuffleForcedMergePolicyTests :
assertSegmentReaders(reader, leaf -> assertTrue(ShuffleForcedMergePolicy.isInterleavedSegment(leaf)));

This assert is supposed to hold after a forced merge:

            writer.forceMerge(1);
            try (DirectoryReader reader = DirectoryReader.open(writer)) {
                assertThat(reader.leaves().size(), equalTo(1));
                assertSegmentReaders(reader, leaf -> assertTrue(ShuffleForcedMergePolicy.isInterleavedSegment(leaf)));
            }