Hmm... Never seen this, maybe because I did the "trick" to get Google Assistant to work shortly after I got my G5+.
Go to Settings - Apps and scroll down to Google (just the app named "Google") and tap on it, then tap Storage and Clear Data, then reboot. If in Settings-Apps-Google your device says "Manage Space" instead of Clear Data, tap that and there should be an option to Clear All Data, select it and confirm, then reboot the device. Google Assistant should show up shortly by long pressing the Home button to activate, it should be Google Assistant now and not Google Screen Search anymore.
Since I did this, I have had ZERO issues with Google search.