Hi @schoen,
I really appreciate your response. Thanks a lot for clarifying this matter. I found potential solving of my problem here : https://www.bennadel.com/blog/3420-obtaining-a-wildcard-ssl-certificate-from-letsencrypt-using-the-dns-challenge.htm. May be it will help somebody else who is struggling with same issue.
Here is also link to issue started by blog owner Does the DNS challenge need to be executed for renewal?.
Your explanation and informations contained in blog fully answered my question.
Thanks a lot once more 