Weird Links Behavior

This is one of the strangest problems I have encountered in Excel, and am
wondering if anyone has any words of wisdom regarding this issue.

I have three files: File A, B, & C.
File A is linked to file C.
File B is linked to file C.

When I open File A alone, it shows the correct linked values.
When I open File B alone, it shows the correct linked values.
But when I open File A, and then File B so both files are opened at the same
time, the linked values in both of them change to a value that is not even in
File C anymore.

The only thing I can guess is that both files might be reverting to an old
linked value somehow.

Has anyone seen this before? Any ideas on what is causing it?

I greatly appreciate your help; thank you.