Are you trying to make a record move (e.g. by button click), which then fires the BeforeUpdate event, then canceling the update and expecting to move to the next record? That's my interpretation. If so, you probably also need this somewhere (probably the BeforeUpdate event, perhaps after the cancel)
If Not Me.NewRecord Then DoCmd.GoToRecord , , acNext
The combobox in question shows blank as I move through the records. However it is a bound combobox. It's rowsource is a query. It's filter property is Yes.
Then there is nothing in its field in those records, or you've applied a filter to it. The rowsource of a combo does not govern what is shown in the combo - that property applies to the combo list rows. The combo can show nothing (because it's bound as as I stated, the field has no value) and in fact you can often add values to the list that are not already there by way of the combo itself.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.