Missing linked files

I have a strange and complicated problem and I'm not sure how serious it is. I use Lightroom CC Classic to store and develop my photos. Occasionally I edit in Photoshop from within Lightroom and a second linked file is generated that when saved in Photoshop becomes a tif file in the appropriate hard drive folder and both files show in Lightroom labelled 1 and 2. I'm sure lots of people do this. Over the past few months SOME (only some of them not all those I generate) of the generated tif files have gone from the hard disc but the Photoshop modified image is the only one that Lightroom shows although it reverts to the original file name not the edit.tif version. Here's the strange thing. When I open the original file from the hard disc it does not show the photoshop generated changes but if I export it from within Lightroom it does. What is happening and where have my files gone?