ECF_OUT variable should be used in situations where job output, is not located in the same directory as job files.
This is necessary for remote job submission when local and remote hosts do not share a common file system.
By using ECF_OUT, the user is then responsible to create the directory structure (all directories) in *advance*, so that output files can be created.
It is enough to copy-paste the directory path for the variable ECF_JOBOUT, and use it to execute the command mkdir -p on the remote host.
ecFlow server is "target agnostic" and does not know on its own how to log appropriately on the remote machine ; it keeps the suite designer responsible for directory creation.