Greetings from Syncfusion.
We have checked the reported scenario and the issue is not reproduced in iOS platform when setting Visual property as Material in the SfExpander. Could you please ensure once whether you have initialized the SfEffectsViewRenderer in the AppDelegate.cs file? We have attached the tested sample.
Please check the below sample and confirm us whether you can able to reproduce the issue in your side. If you still facing the issue, please revert us by modifying the attached sample to reproduce the issue which will be helpful for us to assist you earlier.