Vaadin 14 upgrade to 23 results in blocked mime type

Hallo, I’ve upgraded Vaadin 14 to 23.2.3 using the upgrade guide. Made a clean install. and enabled useDeprecatedV14Bootstrapping. I use Spring boot and Spring security. I implemented my own login page in vaadin with some of the basic components like a combobox.
After starting and loading I’m beeing redirected to the login page, the code is executed but nothing is shown on the screen. Instead I got the following messages.
I tried adding a label: this works, but everything else is not beeing displayed.

Please show us your custom security configuration

new_4.txt (2.7 KB)

So many custom things that could break it… with Vaadin 23 you can extend VaadinWebSecurity which does all of your work and is future proof - see

The solution was setting up spring security in another plain project and copy pasted the things I need instead of upgrading/changing the existing classes.

The only problem is now, that some files are not loaded even if they are correctly placed in the target folder by the build process.