Hi, Mitou. Did you get any progress with your question? I experienced exactly the same. In fact it's much worse and quite random. Sometimes it's thumbnails on the desktop not updated after editing on mobile. Sometimes it's the other way around. Not all photos are like that! So, I'm quite confused!
Same here, some are jsut not updating, but if I open them I see the edits are there.
There is also an acklnowleged (almost 2 years now) but with smatrpreviews from TIF files with "store locally" active. There it works the other way. The thumbnail gets updated, but if you open it for editing it shows the version it had on the initial upload.