I actually managed to fix my problem by trying one of the things you suggested(interacting where the gate should be, which tbh I probably should have tried before). I'll still let you know what happened in case you want to try fixing this issue.
1. I did get the cutscene guiding me back initially. I do have the hill valley key in my inventory as well.
2: Maya is able to run all the way to the end of the screen, but is unable to move to the next area.
3. I never got to unlock the gate, I defeated the Beach Boss and returned to the gate where I found it missing.
4. When I reached the gate, or where it should be, I was able to interact with it and resolve the issue thankfully.
5. I can't seem to upload screenshots unfortunately.