Did you follow my suggestion?
Consider other ways to test your data, to rule out errors.
In a new add-in, create a loop that creates the model lines (all on the same plane with varying coordinates).
I would make the model lines parallel to rule out issues with auto-joining, as that can be a big issue.
You really should post some code - without code it's just a guessing game.
Cheers,
-Matt
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Even your transaction structure can cause issues like this. Please post code if you want in-depth help.
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