In v7.14 this change was made to WG in RouterOS:
*) wireguard - optimised and improved WireGuard service logging;
That resulted in excessive log messages, as you can read from the 7.14 release thread http://forum.mikrotik.com/t/v7-14-3-stable-is-released/174007/1 when RouterOS tries to send handshake packets and the remote peer is no longer available. It did that before 7.14 but the error was not logged so nobody noticed. As you can read from the documentation quote above, you don’t have to explicitly specify the endpoint address and port for RouterOS to initiate the handshake. If a connection was previously established, the current-endpoint-address and current-endpoint-port will have non-empty values and will be used for the handshake.
Now in 7.15 you can enable the “Responder” option and handshake will no longer be initiated by the router.