Why some Site Column can be edited, some can be not?

I have 2 site Column like:

Type: Lookup and point to 2 different Lists already.

I use Country Apply LK for a Content type and Purpose LK for another Content type.

When I edit Purpose LK, very easy, it update.

But when I edit the Country Apply LK, it make an error.

I don't understand how it could be, because two columns are really in the same state.

Please explain to me!