Similar situation as you. Girlfriend denied twice in 2018. She mentioned the interviewers were extremely rude even before she began to talk.
It makes me believe that she was pre-denied based on the online application or the imbecile orange president mandates. The "Interview" was probably a required formality for show.
During the interview, girlfriend had a stack of suggested evidence documents to bring, but the interviewer wouldn't look at them. She had documents that showed she owned her own house, had a decent bank account, was fully employed for many years, had a boyfriend with substantial finances saved up, had letters of recommendation from an employed medical doctor (my sister),
They interviewer said something along the lines as: "How do we know you will come back to Thailand"
GF: "I own my own house, and have worked at my employer more than 5 years, Here take a look at these documents that are proof"
Interviewer: "don't give me those documents, I don't want to see them. Like I said before, how do I know you will come back?"
GF: "I have no reason to stay in the USA, my whole life is in Thailand, take a look at these documents"
Interviewer: "Don't pass me those documents, I don't care."
GF: "When I am in the USA, I will stay at my boyfriend's sister's house. Here is her letter of support."
Interviewer: "I don't want to see it, don't pass any documents through the window please."
Honestly, I was really upset when I heard this. If we were back in the states, if this was any other government agency, we'd probably be allowed to talk with supervisors, examine the employee's style of interview professionalism & fairness, and hopefully get someone that cared. But the US embassy here is a black box by design with no recourse. They could probably huck a loogie right into your face, and there'd be no way to report it.
...sorry for the rant. it's still a sore spot. btw we're married now with a child, so maybe we will get lucky and apply again to showoff the grandchild to the western family.
Best of luck! Sorry I couldn't give any help, lol