Dual Employment issue due to same Joining and Exit Date

Hi ,
I left my First Company on 18 April and Joined second company on same day. Now after 1 Year when i am switching to 3rd company , I got issue of dual employment on 18 April. I was totally unaware about this dual employment thing and I joined a meeting at night in second company after handing over all resources to my first company.
How much this things can affect my career and how to get rid of this thing?

Technically this is a case of double employment, so you need to explain the facts to any prospective employer. Do you have any evidence (like mail or WhatsApp invitation or minutes etc.)? Support your story with that.