Problem with @import in child theme

Autoptimize works perfectly for me, except for a visual glitch in sites that use a specific child theme. The parent theme enqueues a number of CSS files, the last one being style.css. It uses get_stylesheet_directory_uri so the child theme’s style.css is loaded. In the child theme, this is empty, except for an @import statement that loads the parent theme’s style.css.

I’ve disabled CSS optimization -> glitch gone
I’ve excluded style.css -> glitch gone
The parent theme, which loads the same set of CSS files, but loads style.css directly, not through @import, works perfectly.

It appears that the @import statement is somehow causing/triggering the glitch. Any ideas how to fix this? I’d prefer not to exclude style.css permanently for performance reasons.

https://www.ads-software.com/plugins/autoptimize/