Leidos interview questions

I applied online and got invited to the assessment centre straight away. The assessment centre consisted of group work, individual work, and interviews. I liked the company and people and got an offer, but a month before the start date they withdrew my offer. The reason was that I could not pass the security clearance. In the interviews and even when I had an offer phone call I asked them multiple times if I could pass my security test and my foreign nationality would not be a problem. They said everything was fine, but turns out it wasn't. I really hope that they don't screw anyone up like this in the future, I missed other offers and opportunities, and I am so frustrated.

Interview was a part process. First interview was a phone interview asking about technical background and where I saw my career path taking me. Second was an onsite interview going over some circuit analysis, along with some fundamental electronic component questions.