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When you load the iron, try pulling the blade up along the surface of the frog, withdrawing it from the throat and then, while holding it at the upper limit, latch the lever cap. This is just taking the slack out of the blade position on the frog. I don’t have a lot of confidence this will help, but it is a source of backlash and worth at least trying.
Do you have a bare metal upper face on your frog, i.e., not covered in paint or grunge? If not, you can try lapping the face of the frog. You’re just trying to clean it, not change it and not polish it. Coarse is fine.
Is it all of your planes or just one? Can you exchange lever caps to see if the problem follows the lever cap? Is there a hump in it? Does it mate with the cap iron well?