Your tap is tangential to your collector it seems. That's certainly what's bothering us. Try to test to no longer be tangeant but 5mm from the edge for example.
If it works with offset, put your tangeant tap back on and try to make the cut in the manifold before inserting the sheet metal functions.
I repeat my last post: "If it works with the offset, put your tangeant tap back on and try to make the cut in the manifold before inserting the sheet metal functions."
You can also try to cunning by shifting your stitching only by a few 1/10 of a mm to fool SW.
I hadn't seen you took the inner diameter while I took the outer diameter. But for the cuts it seems to me that I need in relation to the outer diameter for the welds.
Indeed it works but hey... It's hacking and then sending it to manufacturing..... If there is no other solution, I will make my sheet metal parts on TopSolid which manages sheet metal much better.