This is intended, you have to learn all traits before using them
Viewing post in Bug in Sex Traits
The problem is 4 weeks in one of my people has only 1 "Unknown" trait in the list and no known traits. I then do a date with intimate talk and learn that trait. Now the list has 6 shown traits that are usable. The 5 previously known but not shown traits have been unusable up til now.
I understand that the 1 unknown trait should not be usable until it is learned but that should not prevent newly learned traits to also be unusable until that 1 unknown trait is discovered.