Strange double edges/halo around objects with 18-55mm

Hi all,

After years of saving up, reading, and all-round excitement, I finally picked up an X-T2 kit last month thanks to the sale. So far I love the camera, and overall I'm satisfied with the results, but I'm not sure about my 18-55mm copy. Occasionally images look quite odd, with a sort of double edge around objects. I do mostly architectural photography, so it's pretty visible around roofs and chimneys, even at 50% zoom. I'm coming from a far older Nikon D70 with its 18-70mm kit lens, and it certainly doesn't exhibit anything similar.

Here's a 100% crop of an example. For reference, the image is f5.6, 1/210 shutter speed, 21mm, ISO 200. At f5.6 this should definitely be in focus. It's not corner softness, but a clear double edge/shift/step/halo.

Full image, where you can see the problem along the entire roof line, even the chimney which is more or less on the same focal plane as the focus point:

This second example is f5, 1/350, 26mm, ISO 400:

On this photo it's odd how quickly it goes from sharp to fuzzy

In both examples you can see the center is sharp, but then deteriorates quickly in the corners with the strange double edges around the chimneys. At those apertures, taking the photos from approx. 15 meters from the subject, with the chimneys only a couple meters back from the focal plane, they should definitely still be in focus, so it's not bokeh.

It shows up in most of my photos, to a greater or lesser extent. Few other examples:

20mm, f5.6, 1/150, ISO 200

32mm, f5, 1/900, ISO 400

The 18-55 is my first lens with OIS, but the photos were taken with OIS off. Still, could it be artifacts from the OIS elements? I bought it brand new, never been dropped, etc.

Any advice much appreciated! This is certainly unexpected, unwelcome, and doesn't seem normal.

Thank you!