Headerimage make Error with https

Hi, i use WP 4.9.4 with Catch Responsive ProVersion: 4.2.2 One day all is fine with https - then next day i call "www.domain.de" but the answer is https but with the note that not all is behind the SSL. If i check i see that is the header image which is not behind SSL. If i go to the customizer and delete the header image and add it again and save, all is fine again. At the moment i dont have any idea where is the mistake. I use similar configuration on the same server but with other Theme - there is never a problem like this. I hope someone can help me... Regards Olaf