Device picked 4G LTE over WiFi

[camedia]

My head unit has both 4G and WiFi turned on and both have strong signals. Speed tests show WiFi is getting only 25 Mbps out of my ISP's 600 Mbps, and 4G speed varies. I downloaded some playlists through Google Play Music in my garage, and only later I found out the download used the 4G connection instead of WiFi. Over the years on my Android phones I have never experienced something like this. On the phones WiFi has always been chosen over mobile connection. It's disappointing because I don't have an unlimited data plan.

Is this something unique to the Joying units?