Thank you for contacting Syncfusion support.
We have checked your reported problem at our end. The reported problem due to on not loading the culture(cldr) file reference for GBP culture.
If you want to use globalization in our component, we should install the cldr data for corresponding culture then use it. Please follow the below documentation to use the Globalaization in NumericTextBox component.
Please let us know if the provided information is not helping you.