11.4.0 unable to import 3M-record external data-file

I think I have it. When you import a file through the Configuration Utility, the file is uploaded to /tmp (this seems to be a function of the Apache web server), which is in the "/" (root) partition. Thus the size of the upload is limited to the amount of free space in the root partition. Once the file is imported to the local file system, it is moved to the /config partition, which may have more space available.

Curiously, if you use tmsh to load a file (tmsh create sys file ifile source-path ), the temporary file goes to /var/tmp, which should have a lot of space available.

I suggest you try the tmsh method