(I also have InDesign 17.4, which I use when I need access to my EasyCatalog plug in. I have had it open a few times this week.)
This issue has just started the first of this year. I started noticing a lot of folders from older InDesign projects inside my In Progress folder with the current date for Date Modified. Each one has only a Links folder and a Document Fonts folder inside. The InDesign file is not there, and the link sets are not complete.
Upon further investigation, the modified date and time of these files matches exactly the date and time of one of my recently packaged files. I also noticed that the Modified Date of the folders inside the top set match exactly the date and time of the earlier-dated main folders.
The original versions of most these files are intact in a different location; mostly archived on a connected removable drive and duplicated on a connected server. But in at least one instance, the original file does not exist in either of those places, as it has been replaced by a newer version.
I am puzzled; I could use some help tracking down the origin of these errant files.