Issue: A customer reports an issue with a production SSAS Tabular instance not starting after reboot. The server has also an SSAS Multidimensional instance which starts just fine. There are no interesting messages in the Event Viewer.
Resolution: During installation, the customer has configured the LogDir of both instances to point to the same physical folder. However, the Flight Recorder can’t start on the Tabular instance because the log file is already locked by the Multidimensional instance. The solution to this horrible problem was to reconfigure the LogDir setting of the Tabular instance (in SSMS, connect to the SSAS instance, right-click the server, and click Properties) to a separate folder.
Moral: Always separate DataDir, LogDir and TempDir folders so each instance has its own set of folders.