That flapper has been blowing/breaking off since they first put them on rvs 50? years ago. If you don't latch them before traveling or in very high winds, just plan on replacing it, it's definitely not something that just started on RWs. In my 40+ years of rving I've probably replaced a dozen of them as have any of you that have rv'd a while.
Danny & Linda
Former '13 FB owner