I’ve had this happen and sometimes it’s a connection issue, other times you need to force quit and restart the app. When it’s a connection issue, for me it’s been because the phone is trying to connect to WiFi that is too far away and the app never loads the data, resulting in the black screen. For example, I have xfinity and can connect to any xfinity WiFi router in the country so long as the owner hasn’t turned off the public WiFi connection, giving me thousands of extra access points pretty much anywhere in the country. Problem is when driving, it will see these networks and never really connect due to distance being travelled, resulting in the black screen issue.
also sometimes the carplay setting in the iphone gets corrupted (can happen) so what I did was "general/settings/carplay/"honda"/"forget this car".... then I would setup car play connection again with the CRV (after I reset the head-unit by long pressing the power button).
Regarding wifi connection, you might want to NOT auto-connect to any wifi. That could be a security risk IMO. While on the road your cell data is good enough unless you don't have unlimited data plan or you have poor cell reception.
i did see that the update from Apple the other day changed my app CARPlay display i my CRV. even though i don't use the maps on my phone and don't have cell data connected for them, Maps pops up on the screen now since the update. have to figure that one out and how to find the text button... that has disappeared. http://www.iphonehacks.com/2019/08/ios-13-carplay-features.html