I drew a structure, used the Structure to Name command to generate a name, then I used the Name to Structure command to generate the structure, but did not get the starting structure.

I drew a structure, used the Structure to Name command to generate a name, then I used the Name to Structure command to generate the structure, but did not get the starting structure. Why?

There is no particular reason to expect this process to work both ways. The name generated by ChemDraw is probably an accurate name for the structure you originally drew. The structure generated from the name is probably an accurate interpretation of the name. The name itself is probably slightly ambiguous, but not incorrect. There are probably other names that would regenerate the original structure. There are also other names that would generate even more dissimilar structures. Currently the IUPAC recommendations offer considerable flexibility when generating chemical names, and that flexibility inevitably leads to ambiguities.