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Lofting Circles and other profiles producing unexpected results
Anytime you are lofting circles or other profiles with differing quantity of corners and line segments be prepared for unexpected behavior.. Onshape is good but it doesn't know where your circles should connect related to each other. It looks like it makes the assumption that it wants to connect the shortest distance between the internal 0 deg of the first circle to the wherever on the second circle at the shortest distance possible. Adding a path can exaggerate this unexpectedness.
This image is just 2 circles (parallel) lofted together. notice it looks like it could be doing it right initially but check out where the pink connection lines are going — opposite sides (shortest distance). This is inducing a twist. Less noticeable with closer sized circles. But you can kinda see the twist here as the middle section is smaller than the smallest end.
Then adding the two circles as connections it puts the connection points on the left and lofts correctly.
Now adding a path with no connections you get the loft doing that twisty thing again.. You can verify the twist with the curve/surface analysis tool.
Adding back in the profiles as connections you get the intended loft without twist.
So next time you are struggling with understanding why your loft is all wonky….It might be twisted and you have to straighten it out with connections.