3D FlipBook - Failed to fetch (sometimes)

Dear all,

I recently installed the plugin on my wordpress site. At first I was getting a 'Failed to fetch error', so I followed the instructions in https://3dflipbook.net/question?id=1313 and got it fixed.

Nonetheless, other people reported having that error, and I have noticed that with the same browser in incognito mode, the error resurfaces.

Looking at the console I get the "Access to fetch at XXX from origin XXX has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled."

I checked and the htaccess file still has the CORS lines, any idea on how to proceed?

Thanks in advance