XMLHttpRequest on https website

After i loaded a stl file and recived an estimation, if i refresh that same page again i am getting this error in console (it disables my https):
XMLHttpRequest cannot load https://site.ro/xxx/p3d/1488401457_phone_holderxx.stl. Redirect from ‘https://site.ro/xxx/p3d/1488401457_phone_holderxxx.stl’ to ‘https://site.ro/xxx/p3d/1488401457_phone_holderxxx.stl’ has been blocked by CORS policy: No ‘Access-Control-Allow-Origin’ header is present on the requested resource. Origin ‘https://site.ro/’ is therefore not allowed access.

Is there a way to make it load that resources over https and not http ?
Thank you.