I thought mine was broken, and was about to take it to the dealer when I made one last ditch effort to figure it out. I have a Pixel 3 with a significant case, and once I figured out how to position the phone, it charges every time, with the case attached.
I put the phone in the slot sideways, push it all the way to the drivers side until it bumps the wall, then slowly ease it toward the passenger side until the blue light comes on. I have to creep it about 1/2 an inch and then it comes on. Works perfectly on my truck, but it was so finicky that I thought it was broken. It's very position-sensitive.
Try that method with the screen facing you, and alternate it with either the left side of the phone facing up, or the right.
