"When using a UMG ListView widget, there seems to be two ways to be notified of item selection changes. An event on ListView which fires when the selection state of any item changes, and an event on the UserListEntry interface which according to the documentation is supposed to fire when the selection state of the item associated to a given entry widget changes. However, that second event never seems to fire."
UserListEntry blueprint interface is newly accessible in 4.20, so this is not a regression.
Also tested and occuring in Main CL 4302610
Example Project Attached
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-63179 in the post.