Salas O'Brien interview questions

Interviews went well. They seemed friendly and professional. The first two interviews were virtual and the third was face-to-face. At the end of the face-to-face, the hiring manager said he would like to make me an offer and that he would bring it to management and get back to me. I followed up via email to confirm that I was excited to come on board and looking forward to receiving the offer. I followed up a week later and was told they would get back to me. A few weeks later, I got a rejection email and when I questioned it, they said it was a mistake and I should disregard it. A few days later, HR called to clarify for me that I was actually one of several candidates being considered (despite the fact that I was told to expect a written offer). After that I was ghosted by them. No explanation, nothing. Very frustrating.