Reset (Clear Out) ComboBox on UF

Hi - I've got a UF with a couple of Comboboxes.
Combobox2 is dependent upon the value of dropdown in Combobox1.
For example; combobox1 has "AFC"; "NFC" in the dropdown. Combobox2 will have a drop down of all the teams in either the AFC or NCF selected in Combobox1.

Here is my problem, everything works fine on the UF, however, when I re-run the UF the next time, the team in Combobox2 is still appearing.
I have the following code:

Private Sub UserForm_Initialize()
CB_1.ListIndex = -1
CB_1.Value = ""
CB_1.Text = ""
End Sub

None of these lines are working to clear out Combobox2. (Interestingly enough, if I exit out of the UF and re-run the UF, then Combobox2 is empty).

If looked online and everything indicates that ListIndex = -1 should work, but it isn't.
Anything I am missing?

thanks,
GRC