I think you might need a fine focus adjustment. I don't know that lens specifically, but most all lenses I have needed a tweak. A couple things to do. Try the test shots using Live View so it's using contrast detect for the focus. Also, use the self timer or a remote release with a delay e.g. 3 second on remote. Don't despair on the K3II. It's a great camera and capable of very nice images. I think you just need to sort a few things out to get dialed in. There's a good article on this site on doing fine focus adjustments here:
Fixing Front and Back Focus - The Remedy - In-Depth Articles. Post back if you ned help on that. You can make your own targets to test on - basically take a page with print on it, angle at 45 degrees, focus on a spot in the center, and see if what's actually in focus is ahead or behind the spot you know you focused on. Adjust the fine tune in the camera then to either bring it forward or backwards as needed. The article goes into detail. I would recommend doing this, FF adjustment, for all lenses.