Yeah famous people were removed. Monroe is so iconic that you probably can't isolate the training data, the same for most presidents or elvis or people like that.
Try throwing some minor variable data into the descriptions of your character, example:
A casual photo of a genuine {23|24|25|26|27}-year old woman, she has an {aquiline|up-turned|celestial|button} nose, and is of {German|Dutch|Belgian|French|Welsh} ancestry.
The actual characteristics don't mean anything in real life, but you can get it to stop being so monotonous in the renders this way. Sometimes a simple change of age changes the template of whatever its rendering.
Another thing to try is t not rely on presets. Professional Photo is especially annoying because of how limited the "look" is. Instead, try "No Style", and hack up the presets. Try taking some of the added tags from 90s photo for example.
Also, telling it to be unique sometimes actually helps. "She has a unique beauty" and so on.
It's really annoying but possible to get it to stop doing what you describe.