Invisible month headings

The [ioya] plugin looks great, but for some unknown reason the month headings for months that contain archived posts are white (and the background of the page template is white), so these headings are invisible. How can this be corrected?

You can view the problem here – https://revivalfocusblog.com/archives-2/.

https://www.ads-software.com/extend/plugins/in-over-your-archives/