I often prefer to use “Loft” followed by “Match surface” over the “Blend surface” tool for the exact same reason. Also, sometimes “Blend surface” will produce inconsistent flow which is most obvious with the Zebra analysis (no matter if the “Interior shapes” option is active or not). Not sure why “Blend surface” fails so often. It was more robust in Rhino 5, despite that its older version lacked the “Interior shapes” option.