Some jars supply pre-calculated Jandex indices. If Weld finds such an index file in the jar it uses that as the input for the scanning for CDI beans
This is normally fine, but I just ran into a case with a Reactive Messaging upgrade when running in EE9 preview mode. The issue is that the supplied index contains javax. annotations to define the bean, while Weld in this mode looks for jakarta. annotations, which results in not beans being found.