I cannot log in a task. Logging in a flow is okay. A task is called using submit.

Hello Kha, you should be able to log in tasks. Here is some documentation on how to accomplish that. https://docs.prefect.io/concepts/logs/#logging-in-tasks

I did exactly as instructed here, but I cannot see the log in a task anywhere. Unless I am looking at the wrong place.

Hello Kha, to my understanding you should still be able to capture the logs when using RayTaskRunner. Are you able to reproduce this example? https://discourse.prefect.io/t/raytaskrunner-freezes-when-writing-data-to-a-local-directory/704/3 . The article also mentions an issue that a user had using RayTaskRunner, and that it freezes when a large number of tasks are run, maybe that is similar to what you are experiencing here? How many tasks are you executing? If the problem persists, I'd also recommend creating a GitHub issue, and sharing a simplified version of your code here for troubleshooting.