Try doing a general search for .ipd files and I mean everywhere on the computer, not the ones Windows wants to do by default.

You search for all .ipd files by searching for *.ipd .

Did you install a new version of DM around the start of the year? Perhaps you then saved to a different folder. Otherwise the only way I've seen the files disappear is to set the data folder in DM to the folder with the data. That completely wipes out whatever is already in that folder. Not sure about the new versions, but prior versions did that.