Clearance process for an intern is the same gruel as for permanent employees. They lack diversity because the more foreign you are or the more foreign connections you have, the more onerous the background investigation and the more likely you are to get questioned. Similar for older people with more experience to investigate but age is less of an issue than being foreign. If your psychobiology profile does not fit the ideal polygraph profile, there's a good chance you will fail the exam for simple reasons like controlling your breathing when anxious if you are used to do that due to training in meditation or other related areas. You can also fail because they badger you to get you to admit to things you never did because the polygraph test results are gospel to them and since they lack better tools, they rely on the results even if they are false. This leads to them attacking your character and pressuring you to the point where you feel like you need to admit something even if you don't believe it or you might question the integrity of your self-image and memory just so you can try searching your mind for a passable answer. The environment is an artificially constructed power imbalance and so nerve racking. Anything you divulge during the interview process can be used against you even outside of the hiring environment. If you value even the tiniest bit of privacy or at any level, this is not the employer for you.

I took an online exam related to data science. After "passing" i had to record myself answering very standard interview questions. Then a very lengthy and indepth background check process.