Find nearby missing photos not working in Lightroom.

I  have been travelling overseas and taken many photos. I was using a Macbook Air and backing everything up to an external drive. On arriving home I have transferred everything to my home PC. I have opened up the Lightroom catalog and started directing all the smart previews to their new location. It was working fine for all the images I took in Thailand and Singapore. I just had to locate one file in each folder and select find nearby missing files and they were linked up perfectly. However I have thousands of photos that I took in Cambodia. Nothing has changed procedure wise. But I can only link them to their new location one image at a time. Find nearby missing photos will not work. This is most strange as they were all on the same external drive and were all moved to the PC at the same time. They were all taken with the same two cameras. I sure hope you can help as to do it one at a time would be a nightmare. Especially as each time I select a new file to locate it goes to the start of the file and not where I last was so I have to scroll and locate each file. It would be an absolute nightmare doing this one at a time.

I have rechecked the files on the external drive with the catalog on my LR catalog also on the drive and all is fine. I just can't understand why all the images taken in 2 countries have relocated just fine and all the images taken in Cambodia are not.