Any reason to think your ADU application would be denied?

I was pre-approved for a loan, 2 days before closing underwriting denied me.

It depends on why you are denying them. 

Both tenants deny it, but we "know" where it's coming from.

If I have multiple qualified tenants that meet my minimum requirements and choose the one that best fits. When I write the other tenants a denial letter do I state that I had multiple applications and the property was...

I have seen before if the roof gets too many layers or weight then might not meet county or city codes and insurance company denies insuring the whole building.

@Ricardo I do, though it was more of a he said, she said situation (he attacked a female tenant after she heard he and the girlfriend fighting and tried to intervene, the female tenant called the police, but of course the girlfriend denied all of it.

Recently there have been municipalities that have set guidelines (regulations) that prohibit denying a tenant for previous criminal convictions at least x-years ago. 

I would deny if it is a multi. 

If you have that covered I can't imagine a bank denying you.