I'm pretty sure we'll be able to correct this. But it could be a little tricky, so we need some details first:
- When you do Library > Find All Missing Photos, do photos from the "original" (first) external drive show up or the "new" (second) one?
- In the, select a top level folder for the first drive, right-click it, and select Show Parent Folder:
Keep doing that until you get to the root folder:
- Repeat that process to show the root folder for the second drive.
- Post a full-resolution screenshot of your entire LR window here.