Help! All of my archived files disappeared!

Help! All of my archived/deleted files have disappeared! Everything in my main level ("Your Work") folder still exists, but nothing in my archive/deleted folder. I don't see anything in "Cloud Documents" tab, either.

I always kept items in the Archived folder that I was not immediately using but planned to refer to in the future. I kept them there for years, so why would they have disappeared now? And more importantly, how can I get them back?

Thanks for your help!