Steps to reproduce:
Add Widget Component
Set any widget class in Widget Class parameter
Set None in Widget Class parameter and notice previous widget class in viewport
After reopen blueprint Widget Component is updated.
I was able to reproduce this issue on our end. I have written up a report and I have submitted it to the developers for further consideration. I have provided a link to the public tracker. Please feel free to use the link provided for future updates.
Link: Unreal Engine Issues and Bug Tracker (UE-44294)
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