A few things.
SMART tests only confirm things about the physical drive but nothing about the file system there.
If your JBOD was assembled as one volume (Volume_1) then by starting the unit with one drive missing (not connected, or lose) you have forced overwriting of the directory structure information. This is why you can't see anything directly, it is also where you get out the backup you made before moving, reformat both drives and restore. No backup then you MIGHT be able to recover your data but equally you might not.
Read the sticky on data recovery (be aware that your disks are formatted with the Linux Ext2/3/4 file system and can not be manipulated directly by a windows computer). I would suggest that you go to the R-Studio site and download their user manual, it will tell you more about data recovery than you want to know but it will also give some idea about what is involved
(we are nor endorsing R-Studio in any way, we have not used their program because we don't use the windows operating system, but they do have a very good manual)