Why would an employer back out of a job offer at the last second?

My issue is as follows. I went to a company three times. Each time the employer seemed very positive. The last occasion he said he would send me an offer.

After 3 days he says that he is not going to send me an offer anymore because of incompatibility issues.

I find this very strange as the last time I saw him he told me he did not say he had any issues and was very positive.

Then all of a sudden when he writes me today he says he has a long list of issues with me, which by the way he didn’t really explain.

I feel like it is something else but he does not want to tell me. I find this strange.

Has this ever happened to you , what do you think is the reason for this?

I think it might have something to do with money as he was trying to find out if i had any other offers line, but I avoided the question because I honestly think that is confidential.

I just find it really weird.

Thanks