Field called "A" appeared in a subform. Not showing up in the builder.

Field called "A" appeared in a subform. Not showing up in the builder.

I have a subform on a form and a field called "A" has appeared within it.

It does not populate in the builder, it does show up in the Application IDE.

I have tried to delete it from the IDE and it keeps reappearing.

How do I get rid of the field without deleting the subform entirely?