Inspecting your project, I see that the icons and some fonts are attempting to load from localhost. That strongly suggests some sort of build issue.
Even though these are not custom widgets, your problem may still be in your custom widget. Errors in a .json file can affect the build in strange and unpredictable ways. I was especially look for trailing commas. I had one trailing comma that broke not only the project I was working on, but also prevented me from creating a new one. Another common error that causes build problems are folders containing no files.
GIS Developer
City of Arlington, Texas