Could be a problem with the CSPs you have assigned in the Developer Cockpit for your application.
If you checkout the tutorial you can see https://academy.mendix.com/link/modules/276/lectures/3194/2.4.2-Creating-a-New-Application---Option-B
If your app is running on MindSphere on EU1 (AWS):
default-src 'self' 'unsafe-inline' 'unsafe-eval' static.eu1.mindsphere.io feedback-static.mendix.com home.mendix.com; font-src 'self' static.eu1.mindsphere.io fonts.gstatic.com; style-src * 'unsafe-inline'; script-src 'self' 'unsafe-inline' 'unsafe-eval' static.eu1.mindsphere.io feedback-static.mendix.com home.mendix.com; img-src * data:;
If your app is running on MindSphere on EU2 (Azure):
default-src 'self' 'unsafe-inline' 'unsafe-eval' static.eu1.mindsphere.io feedback-static.mendix.com home.mendix.com; img-src 'self' static.eu1.mindsphere.io feedback-static.mendix.com home.mendix.com data: uistorageaccountprod.blob.core.windows.net; font-src 'self' data: *.eu2.mindsphere.io uistorageaccountprod.blob.core.windows.net static.eu1.mindsphere.io; style-src 'self' 'unsafe-inline' *.eu2.mindsphere.io uistorageaccountprod.blob.core.windows.net static.eu1.mindsphere.io feedback-static.mendix.com home.mendix.com; script-src 'self' 'unsafe-inline' 'unsafe-eval' *.eu2.mindsphere.io uistorageaccountprod.blob.core.windows.net static.eu1.mindsphere.io feedback-static.mendix.com home.mendix.com; connect-src 'self' 'unsafe-inline' *;
If this is not helping, please open your Development Console (F12) and provide more details from your network stack. There you should find a call to "https://static.eu1.mindsphere.io/webcomponents/v1.17/index.js".