Saint-Gobain interview questions

A very unprofessional experience! I had applied for this position online. I interviewed with 5 managers, 1 engineer and 1 director. All one-on-one detail technical and behavioral questions. I received a written offer letter with a tentative start date in 3 weeks which I accepted. After 12 days I received a call that they have rescinded the offer. No clear explanation about the reason. Lost another option in the meanwhile.

Met recruiters at Campus Recruiting Event, was asked to come back next day for an interview. First interview consisted of behavioral and resume based questions, then asked what I knew about the company and position. Had a final round interview a month later in their office, had 4 different 30 minute interviews with different managers of their department. Asked about resume, what I knew about the position, asked if I had any questions for them.