Feedback from Garmin kindly obtained by the Avionics shop which installed my kit...
"The line style is due to the airspace reclassification effort we began starting in cycle 1706. An airspace can be categorized in multiple ways: by classification and by type and the line style is based on how the airspace is categorized. In this case the airspace is in two main categories in that it is both a Class D airspace and a CTA. For purposes of drawing the line style we have to choose just one of those and as a rule, Garmin has chosen to give precedence to “Class” (D) over “Type” (CTA). If this were a CTA that was NOT ALSO a Class D airspace, we would fall back to just it’s type which would result in the solid line the customer was used to seeing before.
One can still determine that this is a CTA by the “CTA” in the SUA name."