[CI] MixedClusterClientYamlTestSuiteIT test {p0=synonyms/110_synonyms_invalid/Reload index with invalid synonym rule} failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-intake #25461 / 8.17.9_bwc-snapshots
• elasticsearch-pull-request #80154 / 8.17.9_part_6_bwc-snapshots
• elasticsearch-periodic #9255 / openjdk23_8.17.9_java-matrix-bwc
• elasticsearch-periodic #9255 / openjdk21_8.17.9_java-matrix-bwc

Reproduction Line:

./gradlew ":qa:mixed-cluster:v8.17.9#mixedClusterTest" -Dtests.class="org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT" -Dtests.method="test {p0=synonyms/110_synonyms_invalid/Reload index with invalid synonym rule}" -Dtests.seed=495E75E3B56D44B4 -Dtests.bwc=true -Dtests.locale=lv-Latn-LV -Dtests.timezone=SST -Druntime.java=24

Applicable branches:
8.19

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: Failure at [synonyms/110_synonyms_invalid:133]: field [indices.test_index.health] is null

Issue Reasons:

• [8.19] 4 failures in test test {p0=synonyms/110_synonyms_invalid/Reload index with invalid synonym rule} (1.1% fail rate in 368 executions)

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

[elasticsearchmachine]

Pinging @elastic/es-delivery (Team:Delivery)