I had this issue which was previously fixed by editing the etc/fstab file and adding the entry UUID=DRIVE_UUID MOUNT_POINT FILESYSTEM ARGUMENTS 0 1. I did a clean install of OS and now the problem persists again. I have enabled Mount at startup from Disks.
Basically, the hard drive is inaccessible to use for downloading anything, until I go to Files and specifically click on the second hard drive there.
/etc/fstab(file system table) as you did last time? I don't usegnome-disksso don't know how it achieves it's mount – guiverc Oct 30 '18 at 23:56