Missing photos means that the photos are no longer in the location where Lightroom thinks they should be. This can happen if you change the name of a folder, change the name or drive letter of an external disk, or do something else that changes the 'path' to the images. Here's how to fix that: https://www.lightroomqueen.com/lightroom-photos-missing-fix/
I agree that I need to indicate manually the path. But then, there is an option I can tick: "Find nearby missing photos".I have used it for months and it used to retrieve the nearby missing photos within a given date. Now it does not work anymore. I have to create the link for each and every photo, even if it is a "nearby" one, in the same folder, with the same date as the previous photo I manually set.
"Lightroom seems to have an issue in locating the missing photos."
I'm not sure what you mean by this. Lightroom does not do any locating of missing photos, this is not a feature of Lightroom — you the human user of Lightroom has to locate them and tell Lightroom where they are.