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It's too bad they didn't "fix" it by allowing this (where I take Shaun's original code and just delete the constant): Assuming an internal shift-register behavior in the Event Structure, then this "uninitialized shift register" behaves in a perfectly dataflow-like fashion, and it's even simpler to code. Unfortunately, it's also broken, as the Event Structure wont adapt to the type input to the right-hand Dynamic Event Terminal.

Definitely odd, revealing yet another bizarre issue in the land of user events. I will say that technically you are doing it wrong according to the help (which did not change between 2013 and 2017): https://zone.ni.com/reference/en-XX/help/371361P-01/lvhowto/design_case_for_registration/ To "modify" the registration you have to read the wire in from the left hand side inside the case where you modify the registration. Doing that alone with the null ref you had originally did nothing, but adding a registration for a null event did work. My guess, based on this, is that something changed such that the null refnum 'doesn't count' as a proper registration, and so the event structure never registers events until you create one, store it in the shift register, and pass it in on the left. But obviously just a guess. I modified your code according to the help documentation (attached) and it worked correctly on my machine: evnt2.vi