Is not a constructor error when saving working HTML5 file with a different name

I never had this happen before so I am wondering what the problem could be:

errror in console:

TypeError: lib.NAMEOFHEPREVIOUSFILE is not a constructor

(note I removed the actual name of the file for privacy concerns but in the console this is the name of the previous file before I saved with the new name) and this error message occurs when I publish from the new file.

The previous file is still working just fine.

Workflow: I work in sections so when I finish a section, I save the ANCC file with a new name and proceed with the new section.

Never has a problem before but now with this happening I just can't save the file with a new name and continue with this project as usual.

Any idea why this is happening?