@Judi3, I think sometimes a gremlin gets into the works. 😉
I had the same situation twice this summer, when two guests - almost one after the other - requested dates that I had most definitely blocked weeks earlier, because my own family from Canada was coming to visit for 3 weeks, and the period included those slots of time. Hence, I had to decline both requests and then manually re-block the dates. What I do now is check my calendar regularly to make sure that blocked dates remain that way.