Quote Originally Posted by xayoz View Post
if you got a film, you did not clean off the remaining soap properly, keep cleaning and it will be good. But if you got glass, then you shouldn't need to worry about that for a while. I like the ability to remove the plate and flex it to pop off a print, so mine is getting a spring steel plate soon.

As far as glass being a different height in the middle, glass is supposed to prevent that. But yes, you could try shimming it with tin foil or something similar so that it transfers the heat.
Far simpler solution! Move the Z-Axis up. Someone on the /r/ender3 suggested this over shimming it. When you use the glass plate vs the other build plate, you need to move the Z-Axis, otherwise you can't level it correctly. None of the guides/videos I've watched, cover this. Good to know though!