I went further into the rake task rake uploads:recover. I think there is something wrong in the following line:
as far as i understand here all files in uploads/default/original should be added to @paths. However I tried to print @paths into a file and I only see tombstone files is listed.
Am I missing something here? 
@cvx
I think it should be like
concat(Dir.glob(File.join(
Rails.root, "public", Discourse.store.upload_path,
'original',
'**',
'*.*'
)))