If you apply a Gaussian Blur effect to an object and drag it, Illustrator will change the value slightly and restore it back when the transformation is complete.

It seems that Real-Time Drawing and Editing option does not apply the same amount of blur while the drag is in progress.

Especially noticeable if you hide edges temporarily with Cmd/Ctrl + H.

Increasing the blur radius makes the dragged preview blurrier, but still less than the intended value.