Did you create the project using Mendix studio Pro 9.1 or using earlier version of Mendix?
I am still waiting for the answer / solution for my problem. Because of this I am not able to progress with the development. Status quo
First check if you have the correct theme enabled through Project > Settings > Theme in your StudioPro Explorer pane.
If so, it looks like you need to update or reinstall the Atlas module because something is missing or corrupt in your filedirectory {project}\theme\settings.json and widgets folder.
AS per your suggestion, I reinstalled Atlas Core but still some 10 errors are there. Majority of the errors have vanished. I am uploading the latest screenshot