Vaadin Flow in some cases uses class path scanning that scans through all available resources. This is done here https://github.com/vaadin/flow/blob/7e51a3a5a3a9f4b8774201ee0aaf0c7058275a3e/vaadin-spring/src/main/java/com/vaadin/flow/spring/VaadinServletContextInitializer.java#L870-L873 where packages only contains "".

With Vaadin 24.8 + Spring Boot 3.5 + Spring Framework 6.2, the output for a test project looks like

2025-06-25T18:15:29.016+03:00 INFO 25803 --- [ restartedMain] c.v.f.s.VaadinServletContextInitializer : Search for subclasses and classes with annotations took 2633 ms 

With Vaadin 25.0 + Spring Boot 4.0 SNAPSHOT + Spring Framework M1 or SNAPSHOT, the output looks like

2025-06-25T18:14:32.777+03:00 INFO 22966 --- [ restartedMain] c.v.f.s.VaadinServletContextInitializer : Search for subclasses and classes with annotations took 33513 ms 

The number of resources it scans through seems to be roughly the same (10.5K vs 10.9K) so has something else changed that would affect performance 10X? I am not sure even where to begin digging - in Vaadin code or in Spring code.