Thanks for contacting Syncfusion support.
We have tried to replicate the reported issue at our end, but we are afraid that we are not able to reproduce the issue at our end. We have set default value of the binding property and checked the mask value as per your provided value. Please find the sample from the following location.
We have checked with the below configuration
Android Device: Samsung s8 plus
Syncfusion Version: 184.108.40.206
Xamarin Forms Version: 220.127.116.114457
Please share the replication steps like short video and configuration details, etc. This would be helpful for us to give better solution in this.