[CI] :qa:mixed-cluster indices.stats/10_index/Index - all Failure

[davidkyle]

There have been a number of failures of this test on the master branch

https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+master+bwc-tests/1262/console
https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+master+intake/2339/console
https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+master+default-distro-bwc-tests/180/console

In all cases the error is

java.lang.AssertionError: Failure at [indices.stats/10_index:50]: field [indices.test1.uuid] doesn't have a true value
Expected: not null
     but: was null

The failure reproduces if you massage the reproduce line a little by changing :qa:mixed-cluster:v6.4.0-SNAPSHOT#mixedClusterTestRunner to :qa:mixed-cluster:v6.4.0-SNAPSHOT#bwcTest

./gradlew :qa:mixed-cluster:v6.4.0-SNAPSHOT#bwcTest   -Dtests.seed=C06428A7AE0846BD   -Dtests.class=org.elasticsearch.backwards.MixedClusterClientYamlTestSuiteIT   -Dtests.method="test {p0=indices.stats/10_index/Index - all}"   -Dtests.security.manager=true   -Dtests.locale=he-IL   -Dtests.timezone=NZ

The test has been muted in b655c11

#31871 looks the likely cause

[elasticmachine]

Pinging @elastic/es-core-infra

[davidkyle]

The test has also been muted in 6.x df36d1c