Hi Mart,
Alright, thanks for the point & link about Nette, I hadn’t heard of it before.
I did move the entire site as a single zip, so nothing should have gotten damaged, but just to be safe after the issue was encountered, I reinstalled the plugin. All of the filenames were already present in the directory, too, so I don’t believe there was anything corrupted/missing/improperly named. The file it’s looking for for the Widgets class is definitely in the right location, if nothing else.