[CI] CoreWithSecurityClientYamlTestSuiteIT test {yaml=search.retrievers/result-diversification/10_mmr_result_diversification_retriever/Test MMR result diversification multiple indexes} failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-intake #34576 / part4
• elasticsearch-pull-request #120200 / part-4
• elasticsearch-periodic-platform-support #11838 / windows-2025_checkpart4_platform-support-windows
• elasticsearch-periodic-platform-support #11838 / windows-2022_checkpart4_platform-support-windows
• elasticsearch-periodic-java-ea #171 / checkpart4_windows-2025
• elasticsearch-periodic-platform-support #11834 / windows-2022_checkpart4_platform-support-windows
• elasticsearch-periodic-platform-support #11830 / windows-2025_checkpart4_platform-support-windows
• elasticsearch-periodic-platform-support #11830 / windows-2022_checkpart4_platform-support-windows
• elasticsearch-periodic-java-ea #169 / checkpart4_windows-2025
• elasticsearch-periodic-platform-support #11826 / windows-2025_checkpart4_platform-support-windows

Reproduction Line:

./gradlew ":x-pack:qa:core-rest-tests-with-security:yamlRestTest" --tests "org.elasticsearch.xpack.security.CoreWithSecurityClientYamlTestSuiteIT" -Dtests.method="test {yaml=search.retrievers/result-diversification/10_mmr_result_diversification_retriever/Test MMR result diversification multiple indexes}" -Dtests.seed=8CE839E0BA661A72 -Dtests.locale=yue-CN -Dtests.timezone=NZ -Druntime.java=25

Applicable branches:
main

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: java.lang.AssertionError: 
Expected: "second text other"
     but: was "second text"

Issue Reasons:

• [main] 11 failures in test test {yaml=search.retrievers/result-diversification/10_mmr_result_diversification_retriever/Test MMR result diversification multiple indexes} (1.1% fail rate in 974 executions)
• [main] 3 failures in step windows-2025_checkpart4_platform-support-windows (50.0% fail rate in 6 executions)
• [main] 4 failures in step windows-2022_checkpart4_platform-support-windows (57.1% fail rate in 7 executions)
• [main] 2 failures in step checkpart4_windows-2025 (50.0% fail rate in 4 executions)
• [main] 4 failures in pipeline elasticsearch-periodic-platform-support (57.1% fail rate in 7 executions)
• [main] 2 failures in pipeline elasticsearch-periodic-java-ea (33.3% fail rate in 6 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] 11 failures in test test {yaml=search.retrievers/result-diversification/10_mmr_result_diversification_retriever/Test MMR result diversification multiple indexes} (1.1% fail rate in 974 executions)
• [main] 3 failures in step windows-2025_checkpart4_platform-support-windows (50.0% fail rate in 6 executions)
• [main] 4 failures in step windows-2022_checkpart4_platform-support-windows (57.1% fail rate in 7 executions)
• [main] 2 failures in step checkpart4_windows-2025 (50.0% fail rate in 4 executions)
• [main] 4 failures in pipeline elasticsearch-periodic-platform-support (57.1% fail rate in 7 executions)
• [main] 2 failures in pipeline elasticsearch-periodic-java-ea (33.3% fail rate in 6 executions)

Build Scans:

• elasticsearch-intake #34576 / part4
• elasticsearch-pull-request #120200 / part-4
• elasticsearch-periodic-platform-support #11838 / windows-2025_checkpart4_platform-support-windows
• elasticsearch-periodic-platform-support #11838 / windows-2022_checkpart4_platform-support-windows
• elasticsearch-periodic-java-ea #171 / checkpart4_windows-2025
• elasticsearch-periodic-platform-support #11834 / windows-2022_checkpart4_platform-support-windows
• elasticsearch-periodic-platform-support #11830 / windows-2025_checkpart4_platform-support-windows
• elasticsearch-periodic-platform-support #11830 / windows-2022_checkpart4_platform-support-windows
• elasticsearch-periodic-java-ea #169 / checkpart4_windows-2025
• elasticsearch-periodic-platform-support #11826 / windows-2025_checkpart4_platform-support-windows

[elasticsearchmachine]

Pinging @elastic/es-search-relevance (Team:Search Relevance)

[pmpailis]

This is most likely caused by the following docs having the exact same vectors:

 {"textbody": "second text other", "textvector": [0.4, 0.2, 0.3, 0.3], "keywordfield": "test2"}

{"textbody": "second text", "textvector": [0.4, 0.2, 0.3, 0.3], "keywordfield": "test2", "rankfield": 2}

So sometimes, the top-hit for the diversify retriever might differ.

This was also discussed in #142087 (comment) .

@markjhoy could you please take a look at this one and unmute once the relevant fix is in place? Thanks! :)