I have inherited a spreadsheet containing 1500 hyperlinks. It is an index of
docs with 1 link per pdf file.

Some of the hyperlinks were incorrect and I amended them 6 weeks ago.
There are now some incorrect hyperlinks again and where 3 are incorrect in
adjoining cells in same column if I change the first one the other 2
automatically correct themselves.

Is this something to do with how the spreadsheet has been setup?
How can I prevent the unexplainable changes to hyperlinks happening in future?