After having passed my CV, they sent me a list of questions for a written interview, along with a nice mail from a guy who were gonna be my specific contact along the process. I spent 3 days answering all the questions then submitted my file. 15mn later, I received a rejection no-reply email. I reached to my contact to ask how I could be rejected so quickly and why and he answered that it was a mistake. 3 days later, I received the same rejection email again. I asked if it was the real rejection this time and if I could know why but never got any answer

Odd personal questions that have no bearing on being able to complete the task. Get a real sense they're after the "best of the best sir!" yet the pay scale is not anywhere near that demand. Just off the chain logic.