The 4.1.15 version seems to have introduced a bug with the Radzen dialog. It appears to be related to Z position. Top image is 4.1.14 and bottom is 4.1.15.
Make sure you don’t have something in the application ignore list. If you have custom theme Radzen will not run the app and will show message to regenerate the theme by edit application settings and press save.
I've created a new app in Radzen. Nothing in application ignore and no custom theme.
If I add the following to style.css, the dialog is fine. I suspect the z-index was being added in the generated code for dialog but isn't now with the updated dialog.