Steps to recreate:
Just create two textboxes, one with offset and one without: they actually look the same
<TextBox Style="{StaticResource MaterialDesignFloatingHintTextBox}"
materialDesign:HintAssist.Hint="Hint without offset"
Text="Something}">
<TextBox Style="{StaticResource MaterialDesignFloatingHintTextBox}"
materialDesign:HintAssist.Hint="Hint with offset"
materialDesign:HintAssist.FloatingOffset="1,-42"
Text="Something}">