[CI] EsqlSpecIT test {lookup-join.MvJoinKeyFromRow SYNC} failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic #7020 / openjdk21_checkpart3_java-fips-matrix
• elasticsearch-pull-request #62598 / part-3
• elasticsearch-pull-request #62049 / part-3

Reproduction Line:

./gradlew ":x-pack:plugin:esql:qa:server:single-node:javaRestTest" --tests "org.elasticsearch.xpack.esql.qa.single_node.EsqlSpecIT" -Dtests.method="test {lookup-join.MvJoinKeyFromRow SYNC}" -Dtests.seed=6ACADFEF61E87DD -Dtests.locale=rwk -Dtests.timezone=Europe/Ulyanovsk -Druntime.java=21 -Dtests.fips.enabled=true

Applicable branches:
main

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: Expected a list containing
0: expected "Line 2:3: evaluation of [LOOKUP JOIN languages_lookup_non_unique_key ON language_code] failed, treating result as null. Only first 20 failures recorded." but was <missing>
1: expected "Line 2:3: java.lang.IllegalArgumentException: LOOKUP JOIN encountered multi-value" but was <missing>

Issue Reasons:

• [main] 3 failures in test test {lookup-join.MvJoinKeyFromRow SYNC} (0.4% fail rate in 812 executions)
• [main] 2 failures in step part-3 (0.6% fail rate in 355 executions)
• [main] 2 failures in pipeline elasticsearch-pull-request (0.6% fail rate in 354 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] 3 failures in test test {lookup-join.MvJoinKeyFromRow SYNC} (0.4% fail rate in 812 executions)
• [main] 2 failures in step part-3 (0.6% fail rate in 355 executions)
• [main] 2 failures in pipeline elasticsearch-pull-request (0.6% fail rate in 354 executions)

Build Scans:

• elasticsearch-periodic #7020 / openjdk21_checkpart3_java-fips-matrix
• elasticsearch-pull-request #62598 / part-3
• elasticsearch-pull-request #62049 / part-3

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[alex-spies]

Marking this as low risk because it's only a missing warning that triggered the test failure.

@ivancea , do you think you could take a look? You probably understand best where to look.

If this even reproduces - the 2 build scans from pull requests are not relevant, so we really only got 1 failure. (If it doesn't repro, we might just unmute the test if failures are so rare.)