I would’ve originally said that properties exposed on spawn probably don’t work with widgets but you said that structs worked. Thus it’s probably a bug in the engine and handling of enum values. Is it a C++ or a BP enum? Do you have the option to change it from one to the other and see if it still happens?
In any case, a simple workaround is to just have a “Initialize Widget” custom event that takes the enum as parameter and you call that right after creating the widget.
Alternatively (and this is just a shot in the dark), add a 0 second (1 frame) Delay node to your construct event, before the switch.