Intellij Dart Analysis Server Bad State: Too many elements

This error was also causing an issue "cannot find declaration to go to"

After doing a flutter upgrade, I had to do the following:

1. Close IntelliJ
2. delete the project's .idea folder and any *.iml files
3. Reopen the project in intellij

If that doesn't work try File -> Invalidate caches / restart and repeat the steps above