No, working only 3 meters from the origin in mm should absolutely not produce bad stuff. 3 kilometers maybe, but not 3 meters. Something else must be going on.
Yeah, I think the problem was that I set the tolerance to 0.1 units… I was playing with the tolerances earlier, because I got weird results, and forgot to set them back… my fault probably!
I figured it out when this was a result from cap:
And this was the result from fin in the same spot: