Pyrevit doesn't load lots of "ironpython" errors

Installation issues (notion.site) 

Error dynamically compiling pyRevit runtime

What seems to work in most cases:

1. Uninstall pyRevit
2. Delete C:\ProgramData and \%AppData%\ pyRevit folders
3. Move all Revit addinsto a temporary location. Usual addins locations include:
   1. %AppData%\Autodesk\Revit\Addins\<year>
   2. %AppData%\Autodesk\ApplicationPlugins
   3. %ProgramData%\Autodesk\Revit\Addins\<year>
   4. %ProgramData%\Autodesk\ApplicationPlugins
4. [Reboot computer]
5. Reinstall pyRevit
6. Started each version of Revit confirming pyRevit successfully compiled at startup.
7. Moved all Revit addins that were moved in step 3 back to their original location.
   1. you may want to add them one at a time and start a revit session everytime to figure out which ones are causing the issue.