Struggling with third act twist that feels like it ditches the premise

Since the outlining stage, I had a twist planned that was very deliberately made with my theme and protagonist's arc in mind, but after finishing a rough draft it seems to divert way too far from the original premise, feeling almost like a different story, which really sucks. I tried hinting at the twist, and pulling at some parallels from earlier in the script, but my story has a very simple premise that it completely steps away from between pages 65-80 (out of 100 total pages). Peer readers have mostly agreed it was very jarring and did not see what I was attempting to do with it, and I don't blame them, but I really want to keep the twist because in theory it serves the characters exactly how I need.

Should I go back to the drawing board, or are there some scripts that pull off these 'calculated tangents', if you will?