Glass popping out from plastic border

I noticed that my phone’s glass was slightly popping out towards the top from the plastic surround, and when you push it in, it discolours the top of the screen (as if you were pushing hard on the touchscreen itself). Fast forward a month and the glass is popping out so badly you can see the actual backlight shining through the gap. The screen itself still works fine.

I have never dropped the phone except for one time where I tripped on its charging cable. Even so, the screen was still flat. I opened the phone before, only to find out my battery was perfectly fine. It was made in February this year, after all.

What is happening here? I don’t want to spend my money on a whole new screen only for it to still be something else.