Failures are mostly
java.lang.IllegalStateException: Function 'org.jboss.as.test.integration.domain.ReadOnlyModeTestCase$$Lambda$210/0x000000010031e840@787a4519' failed to process in 30 s, caused: "WFLYCTL0379: System boot is in process; execution of remote management operations is not currently available"
30s seems too short since the point of the test isn't to check boot speed.
I'm not clear why this needs custom logic for checking start vs using DomainLifecycleUtil.awaitServers(). The less of that kind of thing the better. Also, the domainClient.getServerStatuses() approach has a race risk, as the master can be started but the slave not connected yet, so you get a successful but meaningless result from the master.