Was is das?

suddenly my geometry went mad. clearallmeshes doesnt help…

another thing. how can i make program to show no gap when it is not supposed to be there because edge line follows another edge line?

I suspect you have internal G1 joints that are confusing the mesher. Unselect everything, run the command DivideAlongCreases, set SplitAtTangents=Yes, then select your object(s) and enter. Better?

If the edges are joined, then you shouldn’t see that gap - you will see the seam line though. If they are coplanar faces, MergeAllFaces should work to merge them onto one single face and eliminate the edge.

thanks. i exploded it and split it manually joined together. my issue is probably a bug in general. confusion of mesher should not happen just like that ?

Yes, this is a long-known issue with the current mesh engine which has never really been improved.