Hey, this isn’t a bug, it’s how the new V2 slash menu works. The /summarize command is hidden from the default / dropdown list because it only shows skills and commands, but it will appear if you start typing /sum... and it gets filtered into the results.
One more thing, /summarize is only available when there’s already at least one message in the chat. In a brand new empty chat it won’t show up because there’s nothing to summarize. That’s why when you reopen a chat from history, it comes back since there’s already an existing conversation.
A similar question was discussed here: /Summarize command not available anymore