I am not sure if this bug is already reported or if it is a dev version only bug.
First, all the clothes are aviables from the start in the studio for me. On the studio -> production -> single scene
And when you change the outfit of a model in the studio, the ethnicity disapear to become "null".
I suppose it is because a "null" appear at the top right when you change the clothes of a model. Indeed if you select / unselect the "is alt" option, the ethnicity replace the null and the model seems to work as intended (it can also reverse a "null" ethnicity to the normal one).
The clothes in the office -> dashboard works without this bug. It just happens if you plan ahead in the studio.