Charles River Laboratories Lab Assistant - Pathology interview questions

I applied online, it was about a month before I heard back for an offer for the first interview. I had the first interview a few days later, which was over video chat due to Covid. I then heard back about a 2nd on-site interview a week later, which I attended about a week after that. I had the chance during this interview to see the lab, observe the processes and ask any questions I had. It was another 2 weeks before I heard that I received a job offer for the position, but after this was where it went downhill. I didnt know how long to expect to wait for a contract that was 'being written', so after about a week I asked for an update and received a slightly rude email in response, so I decided not to ask again for a while. About a week after this they asked me for another 3 references, on top of the two I knew had already been sent as I had confirmed these. I found this a bit strange and concerning, but I had no reason to think I would fail any background checks, as I havent for previous jobs. Overall between the offer and them emailing to tell me that they were rescinding the job offer it was another month. They have given me no reason why, are doing their best to avoid any emails or calls to find out what the reason is.