This got lost in the shuffle during the testing of the latest betas, and didn't make it into the released version, so I wanted to plant it in its own thread, as a feature removal request.
I think it's time to retire the setting on the Images > Advanced tab for Save thumbnails with high JPEG compression quality.
A little history.... One of the original reasons for offering this setting (introduced in jAlbum 8.5.5) was to address a problem in Matrix with applying XBF drop-shadow borders to thumbnails when using certain colors, like red. At lower quality settings, this produced a "mottled" appearance around the thumbnail. Pushing the quality to 90% largely cured it. But Matrix stopped using XBF to produce shadows on thumbnails many, many years ago.
Thumbnail quality was also an issue back when thumbnail sizes were routinely smaller, like 90x90px. Most newer, responsive skins default to 160x160 or higher for thumbnail image bounds, where the image quality is less of a problem.
So now we have three different ways of creating better quality thumbnails - this old checkbox, setting the JPEG Quality for everything to 90%, or choosing HiDPI thumbnails. I believe all current skins can handle HiDPI thumbnails, so anyone wanting better thumbnails can just use that setting. And now we've added the ability to disable chroma subsampling, which requires a quality setting for both slides and thumbnails of at least 90% anyway.
Bottom line - there's really no reason for this obsolete checkbox for thumbnail JPEG quality.