develop7: I'm affected by this issue too. Here's how I've fixed it.
1. Exit GOG Galaxy
2. Go Witcher 3 installation folder
3. Delete/move away goggame-*.* files
4. Run GOG Galaxy client
5. Wait a bit so Witcher 3 becomes "uninstalled"
6. Hit "Import folder" and point to Witcher 3 installation folder.
7. It'll scan existing files and start "downloading", but much much faster -- progress bar will advance ~1G/minute.
Thanks for tip... but it will work without deleting any files. Just move entire folder with W3 to other place (on the same drive to make it quick) and run Galaxy. When it'll loose trace of previously installed W3 game then move again entire game folder to old place (e.g. "c:\GOG Games\The Witcher 3 Wild Hunt\") and GOG Galaxy will automatically find it and recognize as patched to version 1.10 already. Hooray!