I have kind of the same problem in my 2018, but when I plug my iPhone up sometimes CarPlay just doesn't start at all (though the logo is on my phone). I've found that I have to wait until the LEAF's system has completely booted up before I plug in the phone, and then 9 times out of 10 it works normally. Maybe give that a shot, if you haven't already. I believe it's probably something in the firmware that'll need to updated.
2018 LEAF SV