I recently bought this to put in my bike. After a LOT of DIY to remove the old one, which was stuck in the frame and to the handlebars, I finally managed to remove it.

When I tried fitting the new one, the stem seems to get stuck halfway down the hole. I can't see anything in there that blocks it, but it won't go in any more. I tried twisting it and, interestingly, when I twist it to the right, the stem pops up a bit before my downward force pushes it down again.

Does anyone have any idea why this is happening?

I'd appreciate any information to why this could be the case.