When running the EE 9.1 TCK against WF Preview using SE 17 we see three failures:

test=com/sun/ts/tests/websocket/ee/jakarta/websocket/session11/server/WSCClient.java#addMessageHandlerInputStreamThrowsExceptionTest test source
test=com/sun/ts/tests/websocket/platform/jakarta/websocket/server/handshakerequest/authenticatedssl/WSCClient.java#getUserPrincipalTest test source
test=com/sun/ts/tests/websocket/platform/jakarta/websocket/server/handshakerequest/authenticatedssl/WSCClient.java#isUserInRoleTest test source

Unlike WFLY-14915 and WFLY-14916 (which might be related) the jtr reports don't show an obvious common pattern across the 3, so I won't put a lot of details here; best to look at a test run's results.