Without going into a lot of details.. Think of how a Youtube video plays.. Same concept.. Except when Elementum is done, it has the option to keep the fully downloaded file (if you set such in its settings AND if that setting actually works).. gotten reports that for some reason it isn't saving/keeping the completed file after download and I suspect it has something to do with Leia V18. Cuz' I'm experiencing the same thing with Quasar addon on the latest Kodi.. On Krypton, I set it to ask to keep or delete the files.. It works properly as it should every time. However, on Leia (after io error fix), this option isn't working. It automatically deletes the file upon playback completion.

I be doing some more tinkering on why this happens. Though I didn't enable either the "Move finished downloads to separate folder" or the "Keep files after playback/download stops"..cuz never needed them.. so those may be possible fixes..

half finished bits of the whole file is of no use.
fully completed one and saved is good as it is, ready for use.
elementum should be able to do that like quasar but it failed to do so for me, can't save.
need new plugin, i suppose.
the new quasar plugin is working well.
doing what it does, incl saves.

one thing... not entirely sure, need more tests... elementum does a better job with v large files.
quasar fails with big ones (and i remember it has always been the case).
i suspect quasar has some built in restriction that elementum doesn't.