Well, this instance of this encountering of the problem may be solved, but the problem will be encountered again, as the need to re-call UDP.begin() is not documented, and would not be guessed from the current documentation which simply says that the WiFi is re-established.
And, I guess, at some point there should be a call of UDP.stop(). To avoid running into the problem of running out of sockets as @bko mentions here for example.