Recently I posted about the difficulty I was experiencing in moving a file from Lightroom to Photoshop, using the function 'Edit in Photoshop'. I could not get this function to work. Turns out I was using Smart Previews as the original file could not be found, and Lightroom ( or Photoshop) would not allow me to use the 'Edit in ' function to move these files. What led me astray was when I tried another file the same thing would happen. I then discovered to my dismay how many of my files were 'Smart Previews'! Hundreds!
I then set off trying to locate these files so that Lightroom would know where they were. I have spent hours, days and weeks searching. I have also tried to find out how I created this monster. What I have discovered is as follows:
Never move a file in Windows File Explorer, or Lightroom will not know where it is. I remember doing this in my earlier days in Lightroom.
Never interrupt a file moving situation. Wait until the move is finished then do whatever you intended. I remember on more than I occasion while importing files I terminated the import sequence to save time!
I also transferred files to a new computer with faster drives about 3 or 4 years ago. I don't remember what precautions I followed, if any, to ensure that Lightroom would find my files.