There are many reasons (legitimate) reasons why someone could be bumped. Something as small as a cold could prevent being sent. I will wait for additional information before offering my opinion on this.

Probably at the request of his sister.

NASA is an organization of science, but even before that they're an organization of public relations... Calling NASA racist on social media is going to get his sister permanently grounded double-quick if there isn't some kind of proof backing him up...

So i'm not sure this can be blamed on racism. Wonder if we'll ever know why it really happened.

As a factor in any situation that you would find yourself.

when Epps was replaced with another woman seems off-kilter...

I'll reserve judgement until I hear from Epps herself

Most racists would consider her acceptable despite the name - she looks "European Hispanic", not Central/South American, no matter what her actual ethnicity is.
If it is racism, just know they really are that shallow.

However, I suspect there was a change in the mission, because unless there was a medical reason to postpone Ms. Epps, it would typically be due to the changing needs of the experiments and studies they were going to be doing during this period.

Haele

If you google, you'll find a number, including NASA's 12th Director, Charles Bolden.

Here's our friend, Leland Melvin who never spoke, at least not to us, of discrimination at NASA.



https://en.wikipedia.org/wiki/Leland_D._Melvin

With the now famous "Hidden Figures" Mrs. Katherine Johnson...

Epps isn't getting kicked out of the program, she's being postponed to a later flight...

Dr. Epps is an engineer. The person replacing her is a medical doctor. They’re doing more human factors experiments than engineering type experiments.

Link to tweet

There are a lot of discriminatory places in this world, but NASA is way far down the list, and always has been.