I have had my Ender 3 for a few months now and have loved it! I recently noticed that the build plate, the black removable part of the print bed, is sticking up in the middle. If I poke it, it goes back into place, but will not stay there. It shows especially when I print my leveling squares and find the the corners are near-perfect, but the center is crazy thin.
I am using a stock Ender 3 with Cura 4.5.0.
For those who may find this to be helpful, I am looking to find a good replacement build plate. In the meantime, I managed to get mine (without the sticky back) to lay flat by increasing the temperature of the bed from 50 Celsius to 60.