These tests are multi-threaded and doing Sleep() on one of the thread, with verifying that another thread has done or hasn't done something during this interval. However, this is unreliable and may randomly fail, especially if the system is under load.

Suspecting the following tests (although in my local environment I managed to induce the flakiness under stress only for #3, #4, #5):
1. ServiceTestNotInitialized.CheckAutoCleanupCallback
2. ServiceTestNotInitialized.CheckAutoCleanupCallbackFirst
3. ServiceTestNotInitialized.CheckLowDiskCallback
4. ServiceTestNotInitialized.CheckLowDiskCallbackFreeDiskSpaceOnce
5. ServiceTestNotInitialized.UploadAlertsCallback