I wonder if it is a bug or something else, but I can never successfully change the time of gaining a new nationality in the game.

Is it something stops me from getting one?

 

FM 19.0.3 with latest FMRTE.

And I have changed the nationality achieving time to one year in total. But still no one can gain his nationality after one year.

Read that thread again and post all info asked for 

If you are doing as it suggests report as a bug

closing thread no update from user who has been on the forums today.

pm mods if thread needs to be reopened