Any Calendar plugin showing some wrong dates

I’ve been using Event On calendar plugin from Code Canyon. A couple months ago, certain events started showing up under the wrong dates. I thought it was coming from the plugin so I deleted it and reinstalled it and it still picks up the wrongs dates and always for just the same events. I’ve tried three different calendar plugins today and they all pick up the wrong dates for the same events. Where is that info coming from? I never set them up with those dates. Thanks in advance for any help!