external hdd disapeared

I have a hdd attached to my server. It’s sda but has 2 partitions so sda1 @16M and sda2 @3.6T It defaulted to being in the location /media/devmon so I kept that and it worked for ages. Suddenly the data is gone. I had files located here: /media/devmon/4tb_drive/kiwix/zim and that directory is now empty. But I put the drive...