I recently upgraded ArcGIS Pro and got this error when trying to open Jupyter Notebook:
The notebook works fine before upgrading ArcGIS Pro. Current ArcGIS Pro version 2.2.0, Anaconda version 4.3.27 with ArcGIS Pro, Anaconda version 4.4.10 for standalone.
The recent upgrade is causing a number of issues related to the locked environment.
I suggest you add your voice to the chorus by filing an issue with Tech Support through the appropriate channels.