Thank you for using Syncfusion products.
Based on the provided information, we have checked the reported issue "Expander cannot scroll down when loading content with ScrollView & StackLayout" by loading more than 6 Grid layouts inside expander content's ScrollView & StackLayout as you mentioned. We can able to scroll the expander to end and also to top and could not able to reproduce the issue from our end. Please check the sample from the following link,
Kindly check the above sample and let us know if you're still facing the same issue? If not, please modify the sample based on your scenario and revert to us with a complete XAML code snippet and issue replicating video (if possible). It will be helpful for us to check on it and provide you the appropriate solution.
Gnana Priya N