A heavier and slower velocity load will often perfectly center patterns like yours. I have a .410 Dickinson S X S with 30" barrels and fixed chokes. It shot "crossover patterns exactly like yours with 1/2 and 11/16 oz. loads, both of which were running at about 1250/1275, AIR. Shotgunjones recommended I try some 3/4 oz. W-W loads, which were about 1150 fps, I think. He sent me a box actually, bless his heart. I posted the before and after results here several years ago, but the long and short of it is that the slower, heavier payload gave more barrel time and allowed the recoil to move the gun slightly more to the said before the payload exited the barrel. Centered them perfectly.
Until you see it with your own eyes it's hard to believe, but it's real world stuff. The same thing happened to me last summer with a new to me 20 ga. Sterlingworth I traded for, to use on quail and woodcock. I patterned it with 7/8 oz. loads and got the exact results as you, liverwort. One ounce loads at 1175 centered those patterns beautifully.
Thanks again Shotgunjones, my friend. That lesson, and your kindness, will never be forgotten by me.