When using the Replace With option and then undoing it, upon engine restart the Widget Blueprint's UI components are all removed from the Widget Blueprint. It seems the undo is crucial to the issue, since without it I wasn't able to reproduce the issue.
I tested this in both //UE4/Release-4.26 @ CL 14830424 and //UE5/Main @ CL 15183992 and I was able to reproduce in both. I also tested in //UE4/Release-4.25 @ CL 14818863 and this did not occur, so marking this as a Regression.
The button will disapear and you will see "Removed unused Widget 'VButton' " in the Compiler Results.
When restarting the Editor, Widget Blueprints won't clear their UI components on an editor restart
Head over to the existing Questions & Answers thread and let us know what's up.