Example https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/ios-simulator-full-configs/7823

Test Case '-[ReadingListTestCase testMarkMixedEntriesUnread]' started.
2018-07-06 02:22:24.080 xcodebuild[9542:157608] CoreSimulatorService connection interrupted.  Resubscribing to notifications.
2018-07-06 02:22:31.776 xcodebuild[9542:151161] Error Domain=IDETestOperationsObserverErrorDomain Code=5 "Launch session expired. If you believe this error represents a bug, please attach the log file at /var/folders/2j/22s2gz0s7hn48k32d47clxf80000gm/T/com.apple.dt.XCTest/IDETestRunSession-BC20C42D-769A-414A-8F3B-E5EBCCEBC58E/ios_chrome_reading_list_egtests_module-24D7D53A-A8BA-4ACA-9790-83CBC63F0D48/Session-ios_chrome_reading_list_egtests_module-2018-07-06_021913-tcQoGW.log" UserInfo={NSLocalizedDescription=Launch session expired. If you believe this error represents a bug, please attach the log file at /var/folders/2j/22s2gz0s7hn48k32d47clxf80000gm/T/com.apple.dt.XCTest/IDETestRunSession-BC20C42D-769A-414A-8F3B-E5EBCCEBC58E/ios_chrome_reading_list_egtests_module-24D7D53A-A8BA-4ACA-9790-83CBC63F0D48/Session-ios_chrome_reading_list_egtests_module-2018-07-06_021913-tcQoGW.log}
** TEST EXECUTE FAILED **

/b/s/w/ir/src/out/Debug-iphonesimulator/iossim returned 0

1 tests failed and will be retried.

I'm not sure if it's actually the test problem. Assigning to olivierrobin@ to have a look.