ARN region, No space left on device and app crashing. Now some images from volume are lost

That does look promising… Try the following commands first, though, since if you have two or more of these Rails Machines then their volumes are probably all getting increasingly out of synch (as @halfer was suggesting):

$ fly m list -a cstillas
$ fly m list -a cstillas-db

Each of the volumes in the cstillas list (without the -db suffix) may have a different subset of your images…