[CI] ReindexDatastreamIndexTransportActionIT testSettingsAndMappingsFromTemplate failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #6263 / windows-2022_checkpart2_platform-support-windows
• elasticsearch-periodic #6246 / encryption-at-rest
• elasticsearch-periodic-platform-support #6221 / oraclelinux-9_platform-support-unix
• elasticsearch-periodic #6225 / openjdk21_checkpart2_java-fips-matrix

Reproduction Line:

gradlew ":x-pack:plugin:migrate:internalClusterTest" --tests "org.elasticsearch.xpack.migrate.action.ReindexDatastreamIndexTransportActionIT.testFailIfReadBlockSet" -Dtests.seed=837C0E29C0A794A5 -Dtests.locale=pt-CV -Dtests.timezone=Etc/GMT-6 -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_s1] should have finished. Expected 0 bytes for requests in-flight but got 298 bytes; pending tasks [[]]

Issue Reasons:

• [9.0] 4 failures in test testSettingsAndMappingsFromTemplate (1.6% fail rate in 243 executions)
• [9.0] 2 failures in pipeline elasticsearch-periodic-platform-support (25.0% fail rate in 8 executions)
• [9.0] 2 failures in pipeline elasticsearch-periodic (28.6% fail rate in 7 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)

[masseyke]

This one is fixed by #122274