[CI] DataStreamDeprecationCheckerTests testOldIndicesCheckWithOnlyNewIndices failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #9040 / ubuntu-2004_platform-support-unix
• elasticsearch-periodic-platform-support #9033 / ubuntu-2404-aarch64_checkpart2_platform-support-arm

Reproduction Line:

./gradlew ":x-pack:plugin:deprecation:test" --tests "org.elasticsearch.xpack.deprecation.DataStreamDeprecationCheckerTests.testOldIndicesCheckWithOnlyNewIndices" -Dtests.seed=17BD723E3E20BC5 -Dtests.locale=guz -Dtests.timezone=Antarctica/Palmer -Druntime.java=24

Applicable branches:
8.18

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: null

Issue Reasons:

• [8.18] 2 failures in test testOldIndicesCheckWithOnlyNewIndices (1.8% fail rate in 109 executions)
• [8.18] 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]

Pinging @elastic/es-data-management (Team:Data Management)