When I tried Nextcloud, I found there was an option to sync all photos from Google Photos. It synced around 10% photos and reported success. Overall, Nextcloud had lots of breaking bugs/instability issues like that in almost all cases I tried, so I ended up just buying a second account at a different cloud provider, so everything is now synced to 2 providers, in case I lose access to my Google account.

I experienced the bug you mentioned about 5 years ago, I wonder if they ever fixed it.