> Is the problem that unity8 simply continues to use the original cached result
Almost certainly, yes. The thumbnailer will realise that the file has changed an it will re-create the thumbnail for it, but only if someone actually asks the thumbnailer for the thumbnail again.
I suspect that this could be fixed the same way you fixed it during the spring, by appending some suffix to the image URL that changes each time a photo is edited. (A counter might work.)
> Is the problem that unity8 simply continues to use the original cached result
Almost certainly, yes. The thumbnailer will realise that the file has changed an it will re-create the thumbnail for it, but only if someone actually asks the thumbnailer for the thumbnail again.
I suspect that this could be fixed the same way you fixed it during the spring, by appending some suffix to the image URL that changes each time a photo is edited. (A counter might work.)