We also have the same issue, in our case a confirmTransferIntent handler that needs to use LAContext to perform local authentiation
There appears to be some breaking change in iOS13, this capability has worked for several years in our app but stopped working with iOS 13.
So far by analyzing in a debugger I can see that touch/face id authentication works as expected, and that the completion handler is called with INTransferMoneyIntentResponse (INTransferMoneyIntentResponseCodeReady), but Siri does not show the final confirmation dialog to complete the transfer. When I bypass LAContact evaluatePolicy the process works fine.
I've posted a bugreport via Feedback Assistant, including a sample app that readily reproduces this flaw. FB7414145
It's same iOS 13.3 beta 2.