Hi Martin, I'm not really sure exactly what's going on there, but I was able to get the attached solid version after rebuilding both the magenta piece and the smaller tube on one side of it all in one loft with the "straight sections" loft option.

Something seems to be getting confused for whether one of the previous edges was a closed curve or not, something like that.

Anyway I hope the attached solid version gets the immediate problem solved.

- Michael