Thought I'd mention this as it might be by design: the slack notification utilities used to work with prefect core alone, but after 0.11.5 they seem to require prefect cloud/server. I discovered this issue when trying to upgrade to 0.13.x in my quest to get my team's existing code to work with prefect server.

Hmmm, that sounds like a bug. Would you mind reporting an issue with details on how to reproduce your issue? https://github.com/PrefectHQ/prefect/issues