~30 failures in the past two months

Build scan:
https://gradle-enterprise.elastic.co/s/lgmcz6ol5jdvk/tests/:qa:mixed-cluster:v6.8.17%23mixedClusterTest/org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT/test%20%7Bp0=indices.split%2F20_source_mapping%2FSplit%20index%20ignores%20target%20template%20mapping%7D

Reproduction line:
./gradlew ':qa:mixed-cluster:v6.8.17#mixedClusterTest' -Dtests.class="org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT" -Dtests.method="test {p0=indices.split/20_source_mapping/Split index ignores target template mapping}" -Dtests.seed=240DCD1B0C321576 -Dtests.bwc=true -Dtests.locale=ar-SY -Dtests.timezone=Asia/Dhaka -Druntime.java=8

Applicable branches:
master, 7.x, 6.8

Reproduces locally?:
No

Failure history:
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT&tests.test=test%20%7Bp0%3Dindices.split/20_source_mapping/Split%20index%20ignores%20target%20template%20mapping%7D

Failure excerpt:

java.lang.Exception: Test abandoned because suite timeout was reached.

  at __randomizedtesting.SeedInfo.seed([240DCD1B0C321576]:0)