The app does not start up with a dark screen

Unity Engine
,
1

We received a report from a user about an app that is being released that the app does not start up with a dark screen.
This app has been confirmed to work properly.

The user ’s device

iPad mini2
iOS 12.1.4

is.
I received a report that other apps are working without problems, so it does n’t seem to be a malfunction of the device.

I want to know when this phenomenon occurs and how to deal with it.

Development
Unity 2018.3.13f1
Xcode 10.1 (10B61)

is.
FirebaseSDK is implemented in the app.

Thank you.

2

I have the same problem.
There is a problem that the app does not start from iPhone iOS 15.
After starting it about 3 to 10 times, the app is launched.