I have face this issue, so I have my solution for it 
Here is a small trick to download all the files from any index.
open the page

make sure pop up is allowed for the page
paste the javscript in console
var a = document.getElementsByTagName('a');
for (var idx= 0; idx < a.length; ++idx){
if(a[idx].className == "list-group-item-action"){
console.log("I AM NOOB",a[idx].href.slice(0,a[idx].href.length -7));
window.open(a[idx].href.slice(0,a[idx].href.length -7),"");
}
}
hit enter
then if everything goes fine then files will get download

The code is self explanatory, so change the class name according to the index and make it work.
P.S I have tried and tested, and it might not work if file download quota is exceeded
Here is a small trick to download all the files from any index.
open the page

make sure pop up is allowed for the page
paste the javscript in console
var a = document.getElementsByTagName('a');
for (var idx= 0; idx < a.length; ++idx){
if(a[idx].className == "list-group-item-action"){
console.log("I AM NOOB",a[idx].href.slice(0,a[idx].href.length -7));
window.open(a[idx].href.slice(0,a[idx].href.length -7),"");
}
}
hit enter
then if everything goes fine then files will get download

The code is self explanatory, so change the class name according to the index and make it work.
P.S I have tried and tested, and it might not work if file download quota is exceeded