There is a strange bug, when creating an animation with "create movie file" turned on.
Normally,when starting an animation render, a folder is created,the images populated inside and when finished the movie file is created.
This only works with renders in preview mode.Choosing Fast or Accurate Mode don´t create a folder, instead it uses the main folder (images in my case).
When starting creating the movie file, every file (not folder) in the main folder is deleted, not only the rendered movie files.
Render into a manually created folder will delete it when creating the movie file.
Only workaround is to uncheck the "create movie file".
Visualize 2017 Pro SP4