Disappearing monsters

This has happened to me constantly during this event – I will find a monster pig & it will disappear. I have had them disappear before I could fight, I have had them disappear after I fought. Never get any credit and they vanish from the log – most of the time. Sometimes they will disappear before I can fight them and then 2 hours later they show up as a loss even though I could never see the boss again. This game is terrible.