[CI] ReindexDatastreamIndexTransportActionIT testSettingsAddedBeforeReindex failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #6207 / ubuntu-2004_platform-support-unix
• elasticsearch-periodic #6218 / openjdk21_checkpart2_java-fips-matrix

Reproduction Line:

./gradlew ":x-pack:plugin:migrate:internalClusterTest" --tests "org.elasticsearch.xpack.migrate.action.ReindexDatastreamIndexTransportActionIT.testSettingsAddedBeforeReindex" -Dtests.seed=8DA96413479CD20 -Dtests.locale=en-HK -Dtests.timezone=America/Maceio -Druntime.java=23

Applicable branches:
9.0

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: All incoming requests on node [node_s2] should have finished. Expected 0 bytes for requests in-flight but got 298 bytes; pending tasks [[]]

Issue Reasons:

• [9.0] 2 failures in test testSettingsAddedBeforeReindex (1.6% fail rate in 124 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)

[parkertimmins]

Fixed by #122274