It’s becoming a lot more common. This also happened to me once, and I hated it.
I was working in a high-level position and been hired in under a job description that inaccurately had the word Assistant in it. This was never an issue because it was clear that I wasn’t doing ‘Admin Assistant’ work, but things got messy when we hired a new Director.
The woman was from an extremely conservative background and seriously had it out for me. She didn’t really like that I had aspirations that extended far beyond my position or that I had more education that she did. When she reviewed my job description she decided that she needed an admin asst and that per my job title, that was the work I should have been doing. She became very assertive about enforcing it.
She temporarily demoted me from complex analyst-level work to scheduling her travel, taking dictation, typing up her letters and handling her phone calls. This was a power move done to prove something. I was miserable, I fought back and it was a battle every day. She didn’t get away with it though, and it turns out her personality wasn’t a good match for our culture. She left only a few months after that.
I did learn something from it though, and looking back wish I hadn’t kicked and screamed about it and had presented myself as more flexible and adaptable. In the big picture I think I would have looked like the better person.
In your situation I’d say roll with it, be cool about it at first and really see what the position has to offer. Process-driven roles like IT PM can be tedious, but you also have a little bit of flexibility in how you manage those projects. In the short -term, get a few small projects under your belt that you can list on your resume as successes, and then start marketing yourself somewhere else as your previous role, who now has successful PM skills. It could potentially take you further.
Good luck, PB. I know this may be a frustrating time but ride it out and just keep collecting paychecks until things settle. Then make some decisions from there. As someone who was recently very, very unemployed, I wish I had your opportunity as opposed to the one I was dealt.