Size Limitation for MyCloud web interface?

I’m using the web interface MyCloud (files.mycloud.com) to upload files to my PR4100 at home while away.

Small files work fine, but when I try to upload a larger file (20 gb), nothing happens – no error message, nothing.

What’s worse, the upload files button no longer does anything. Clicking on it no longer brings up Finder to choose a file. The page has to be refreshed.

Is this a known problem or what?