There was a lot of little UI changes, that’s why that fix was released as soon as possible.
But basically you want to migrate the changes from the OnDrop() functions and you also want to make sure when you drop the Widget you are adding it to the canvas panel and not just back to the viewport.
If you add it simply to the viewport it won’t belong to a layout and won’t have an overridden OnDrop() function. If you are using the UI from launch day and have not made many changes to the UI in your project I would highly recommend migrating the UI with the changes.
I’m happy you were able to solve the issues, please let me know if it cleared up your continuous build system cook errors.