This is an error one of our users was running into:

import ray
@ray.remote
def f():
  return 1

ray.shutdown()
ray.init()
ray.get(f.remote())

And ray will print:

This worker was asked to execute a function that it does not have registered. You may have to restart Ray.

Shutdown will clear the function cache and therefore ray.init won't register the right functions. This looks like a user error, but I can see what they are trying to do (making sure any other ray instance has shut down properly I guess).

This is not a bug I think but we might want to print a more informative error message here. And hopefully this issue will point people into the right direction too if this happens.