transparency

if “Load WebP or AVIF in supported browsers?” is on, .png files with transparency will loose that transparency in browsers that support AVIF due to a recent technical change in Shortpixel’s AVIF toolchain.
Shortpixel is looking at alternative solutions, but until then as a workaround you can either:

• add .png to Autoptimize’s lazyload exclusion field
• or to use below code snippet to disable AVIF images;

add_filter( 'autoptimize_filter_imgopt_do_avif', '__return_false');