When RAD Studio 10.3 Rio applications are executed on Android 9, you get an intermittent error due the call of a restricted API. As an example, this is reported at https://quality.embarcadero.com/browse/RSP-23008.
The issue is a call to a restricted platform API in FireMonkey, we are looking forward to remove in a future release.
There is a fairly simple workaround. The message is not displayed to the user (but only in the internal logcat) if you modify the TargetVersion parameter in the AndroidManifest XML file, setting it to TargetVersion = 28:
If you have an existing 10.3 Rio project for Android and you want to target Android 9 Pie, you should update the manifest file accordingly.