2.4.1 is here: https://downloads.www.ads-software.com/plugin/post-thumbnail-editor.2.4.1.zip
The reason why I ask is that there were really minimal changes between 2.4.1 and 2.4.2, so the problem was probably introduced between 2.4.0 and 2.4.1. However, I don’t think that there were any javascript changes there, which appears to be the problem that you’re having. I’m really kind of stumped as to the exact issue that you have.
If you use < 2.4.2, just know that there is a security issue that was solved, where a logged on user could potentially delete thumbnails if they were tricked into specially crafted link. I’ll try using the windows version of safari, but if you could tell me which plugins you have enabled and your theme, I could try that too.
Thanks for your help