Hello Tom!
In order to see crop changes you need to clear the cache of your browser after you made a cropping (e.g. in Chrome and Firefox you can do it by pressing Ctrl+f5). This is how thumbnails look without cropping in my example of gallery https://prnt.sc/fb6eoh and this is https://prnt.sc/fb6fag how they look with cropping (Bottom Right, Top Left, Center Right) after I refreshed the page using Ctrl+f5 in Chrome.
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