@docinfo It happens that images converted to WebP are not smaller than the original ones. Then such images are skipped. You don’t have to worry about it. This mostly applies to very small images or images that have previously been compressed. Skipped images do not use up your limit.
If you want to force all images to be available in WebP and AVIF, then in the plugin settings, in the Advanced Settings section, disable the “Automatic removal of files in output formats larger than the original ones” option.
Please remember that one image in the limit means one conversion process (not one file in the Media Library). All files on the disk are counted (e.g. files from the /uploads directory). One image on disk uses two conversion processes from your limit because it is converted to both WebP and AVIF. All images you have on your website (on the disk) are counted along with any other sizes generated by WordPress. One image in the Media Library means several or more than a dozen files in the /uploads directory, because WordPress automatically generates additional files from one uploaded file, in different sizes.