Yes, undoubtedly the creation of a new group broke the iterator.   That sort of thing happens a lot, and it goes back to the underlying operating system primitives.   For example, I’ve found that when iterating through files and directories in Microsoft Windows (regardless of language), you mustn’t create/remove files or directories while doing so.   First complete the scan (e.g. of one complete subdirectory), then act upon/iterate through an in-memory list of the things that the scan finds, and all is well.