Puzzles with incorrect structure at 0 kcal?

Just posting because I’m curious to know what’s happening. (Please forgive me if this topic has been covered already.)

In my quest to conquer the Eterna 100, I’ve come across two puzzles in which I’ve found a sequence that leads to 0 kcal for the natural/target delta but does not stabilize the target structure. In tutorials and from what I’ve learned from other players, it seems like the expectation is that natural/target delta can be used as a guide and that when it reaches 0 kcal, the target structure should be stable. So what’s different about these puzzles? If anyone else has more examples, I’d interested in those too.

When evaluating the energy of your sequence in both the target mode structure and the structure found in natural mode, the energies are equal. This means that there are two structures, including the target structure, which are both equally likely! The folding engine had to choose one of them as “most likely”, and it happened to chose the one that wasn’t the target.

Interesting. This seems to be a somewhat rare occurrence. Is it more likely to happen when the target structure is symmetrical, as is the case in both the Bullseye and Snowflake 3 puzzles?

The 0 kcal with red still showing actually happens quite a bit, usually on puzzles that need blocks to complete. . I always thought it was due to rounding errors. Symmetry usually doesn’t do it. I can always find another solution that works. I wouldn’t change anything as far as the kcal calculation works.

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