Forcepoint interview questions

Interview process was pretty standard: Initial phone call with the HR, multiple Zoom video calls with Team lead and the System Architect. Then asked for an on-site interview, later it was changed to Zoom as well as of low budget/whatever issue. As with any Salesforce developer interview, we can expect a lot to be asked for, including previous project use cases, technical questions with some scenarios, behavioral questions and some simple definitions. I was pretty confident after each round(overall 5 rounds) as things seemed to work well, with any given technical scenario I was able to answer confidently. As every round went well, I have heard the offer confirmation from the HR via a phone call, discussed the salary, and even HR provided me with some website/tool that provides the living expenses comparison to negotiate well. And after all this phone calls/emails, they couldn't provide me the actual job offer. However the hiring department is pretty confused with my work authorization even though I have explained everything with providing proper documentation. I mean, if they had any issues with regards to work authorization, they should've mentioned that in the first phone call like a month ago, right? But not after all technical rounds and even salary negotiations. This is very unprofessional way to treat candidates. They cannot have people in the HR department who doesn't even know the basic work authorization stuff. I never had/heard this kind of recruiting process in any big/startup company. If anyone is getting an interview scheduled with this firm, please make sure to discuss everything prior to the technical rounds.