I will admit, I've never seen this error before. I've always thought the "Sakura used Smash" text messages were just flavor and not actual barriers to inhibit progress to other zones. I suspect this is probably just an error you're experiencing and that you should probably just refresh the game and try again.
Please let us know if this problem persists once you've refreshed. If it does, try swapping some ninjas in and out of your team.
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