After installing the patch for ArcGIS Pro 2.8.1, every time I launch an ArcGIS Pro project that has an existing Python Notebook the active Python environment changes back to arcgispro-py3. The only thing that changed was installing the 2.8.1 patch. I have tried reinstalling ArcGIS Pro and cloning to different locations, but as soon as I open that notebook the active environment changes back to arcgispro-py3.
The notebook previously used a cloned environment with no issues.