[CI] FileSettingsServiceIT testSettingsAppliedOnStart failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #11153 / debian-12_platform-support-unix
• elasticsearch-periodic-platform-support #11083 / oraclelinux-8_platform-support-unix

Reproduction Line:

./gradlew ":server:internalClusterTest" --tests "org.elasticsearch.reservedstate.service.FileSettingsServiceIT.testSettingsAppliedOnStart" -Dtests.seed=E3DF8A2E9B24A412 -Dtests.locale=kln-Latn-KE -Dtests.timezone=NZ-CHAT -Druntime.java=25

Applicable branches:
9.1

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: null

Issue Reasons:

• [9.1] 2 failures in test testSettingsAppliedOnStart (0.7% fail rate in 267 executions)
• [9.1] 2 failures in pipeline elasticsearch-periodic-platform-support (18.2% fail rate in 11 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)

[elasticsearchmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[mosche]

see #131160, #131210

latest attempt to fix: #134368