Reading doubles (numbers) in and out of Excel cells

I'm reading in values from an Excel sheet and have the user checking those numbers/text and hitting save again if they are correct. It works well for any text and numbers, except for my discount being of double type.

Private Sub UserForm_Initialize()

' filling form
TextHN.Text = Range("D3")
'...
' original: TextDP.Text = Range("D7") - but wouldn't read in 12.5
' therefore tried below as well
 Dim new_value As Double
    If IsNumeric(Range("D7").Value) Then
        new_value = CDbl(Range("D7").Value)
        MsgBox new_value # displays 12.5
        Else
        new_value = 1
    End If
    TextDP.Text = CStr(CDbl(new_value))
    MsgBox TextDP.Text # displays 12

I read several articles (Convert TextBox.Value to Double into VBA (Excel 2013) & https://www.mrexcel.com/board/threads/textbox-value-to-double.1066876/), but nothing helped. How do I need to change my code to display my discount in TextDP? (I can read it out as double into Excel file fine)

Update with screenshots:

I'm surprised that it displays it for hospital name and abbreviation correctly (and saves it accordingly), but not for discount percentage and expiry length...

Evidently, SpinButton's or else code affects TextBox's content.

Highly likely, the TextDP_Change event is handled to setup related SpinButton. Then SpinButton_Change sets TextDP back.