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"It has been since" is referring to a point in the past. In fact, "since" always requires a specific time in the past, not a continued time period, as described by Cambridge Dictionary. A simple past is a better fit.
It has been a year since I started consulting Dr Wade.
It has been a year that I have been consulting Dr Wade.
In the first sentence, you are talking about your starting point of the consultation: a simple past event. In the second sentence, you are talking about your continued engagement up to now: a present perfect.
