user needs edit permission to load js files in Site Assets directory

We have a classical Sharepoint site whose form is custom built with content link in content editor webpart in a page. 

When the page loads, it needs to load the css, js files in Site Assets directory to render the page. 

Users were able to get the page loaded fully with read permission until last Sunday night. 

Now we have to give users edit permission to Site Assets to load page successfully. 

At console log, we can see with edit permission, all required files are loaded while with read permission, no log of required files but no error. 

Could someone advise what might happen to cause this? How can we remediate this? 

Thanks a lot in advance.