The cheapest fix is to keep smoke rendering at quarter resolution, but add a 1px depth-aware dilation/repair during the final upscale.
If a smoke pixel was cut out, but a neighboring pixel has valid smoke alpha and the full-res depth says the current pixel is not behind the wall/window frame, softly pull a little alpha from the neighbor.
The reason is the depth filter. For performance, smoke uses a quarter-resolution depth/mask, and the final upscale or AA cannot fix the artifact because the pixel has already been cut by the depth filter.
The easiest way to reproduce it is to throw a smoke in Mirage window and inspect the pixels along the top edge.
The depth filter is needed because the smoke volume intentionally overextends into map geometry to close small gaps. If you look at the window from a 90-degree angle, you can physically see where the smoke volume really is - beyond thin wall. From the front perspective, that overextension is hidden by the depth filter.