Three months after posting this issue to the DJI Customer Support Forum the same problems persist with the final release version of Android Pie on the Pixel 2 XL.
DJI Go App force-closes immedeately on startup, requiring full uninstall, re-install, a full re-download of application resources and setup in order to fly again. Next day have to do it all over again and again.

So far, no indication that DJI is working to resolve.

Pixel 2 on Android P Beta (App Crashes)

Perhaps the DJI developers haven't tested the app with Android 9 very much. DJI Go 4 is coded for Android 4.4 (Kitkat, API 19) minimum and is probably tested on Android versions up to 8.0 (Oreo, API 26), so I'm not surprised.

In my region and phone provider, Android Pie has been officially deployed (no longer beta) and yes it has broken DJI GO 4 (Spark) and DJI GO (Osmo Mobile 2). Crashes on start up.

I have exactly the same issue! DJI go just crashes, won't open.
It works when you install it, as soon as you reboot the phone, bye bye app! You have to uninstall and reinstall it..and don't dream to restart your phone