From support case:

The attached demo WAR (source) contains two identical web services classes in different packages, which corresponds to our versioning layout used in production. Both web services use the same handler class. However, the handler's PostConstruct method is only executed for invocations of one of the two web services (expected: for invocations of both web services).

This error could theoretically be worked around by renaming one of the web services, or by changing one of the target namespaces. However, this is not an option for our production purposes.

This error did not show up in EAP 6.4.9 and earlier versions.

Essentially they have two webservices both annotated identically with:
@WebService(name = "DemoService", targetNamespace = "http://demo.svc.co.at")
but they are exposed at different URLs through their web.xml file

In EAP 6.4.x this works fine. In EAP 7.x only one version calls PostConstruct method, presumably the first one deployed. So, this appear to be a regression.