Strange my mix 4 is charging fine, 120w 22 mins, although i have lost the boost setting in the charge menu, used to get 17 mins with that, not sure if thats a bug or it was removed for some reason.
I noticed for whatever strange reason it will not use the default chosen sound setting for each app, i have to go to each individual app, and select the sound and apply, very odd indeed, never seen anything so complicated to configure in my life.
I am having the same issue on the MIX 4, works fine but as soon as the phone locks nothing, its a pest because i control all the lights in my house with it. Sure it will be fixed soon :)