I’ve just had this problem after an update and I solved entering File/Settings/Plugins. Then at the top of the window there are two options: Marketplace and Installed, then I clicked on Installed and on Flutter plugin there’s was message saying that the current version of Flutter does not support the new version of Android Studio, so there was a green button Written “Restart” then I clicked and when It opened again, the problem disappeared. May not be the same for you, but many people will search for it here and may help someone.