Subscriber download fail

I’m trying to download my subscribers as a CSV file, but clicking ‘Download new’ or ‘Download all’ just brings up a white empty screen. The download doesn’t actually happen.

Any ideas how to fix this?

I've tried an email the creators of this service once used to chat to me, but it's now failing. A worrying sign they've lost interest in this site and it's just going to slowly fall apart now?