[CI] MlWithSecurityIT test {yaml=ml/evaluate_data_frame/Test regression with null metrics} failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #6103 / ubuntu-2004-aarch64_checkpart4_platform-support-arm
• elasticsearch-periodic #6114 / openjdk21_checkpart4_java-matrix

Reproduction Line:

./gradlew ":x-pack:plugin:ml:qa:ml-with-security:yamlRestTest" --tests "org.elasticsearch.smoketest.MlWithSecurityIT.test {yaml=ml/evaluate_data_frame/Test regression with null metrics}" -Dtests.seed=C6F0814C26B0B49E -Dtests.locale=en-IM -Dtests.timezone=America/Nuuk -Druntime.java=23

Applicable branches:
8.18

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: Failure at [ml/evaluate_data_frame:3]: expected [2xx] status code but api [indices.create] returned [503 Service Unavailable] [---
error:
  root_cause:
  - type: "unavailable_shards_exception"
    reason: "at least one search shard for the index [.security-7] is unavailable"
    stack_trace: "org.elasticsearch.action.UnavailableShardsException: at least one\
      \ search shard for the index [.security-7] is unavailable\n"
  type: "unavailable_shards_exception"
  reason: "at least one search shard for the index [.security-7] is unavailable"
  stack_trace: "org.elasticsearch.action.UnavailableShardsException: at least one\
    \ search shard for the index [.security-7] is unavailable\n"
status: 503
]

Issue Reasons:

• [8.18] 2 failures in test test {yaml=ml/evaluate_data_frame/Test regression with null metrics} (1.4% fail rate in 140 executions)

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

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)

[slobodanadamovic]

Resolved by #121664