Hellow! Sorry for my English)
I have a trouble with gallery:
i have a folder Photos, for example. If i look it in browser gallery creating previews for all pictures in this folder and save it in …/nextcloud_data/username/thumbnails. But when i share it to another user and he is looking it in browser gallery greating same previews in his thumbnails folder. It makes one job two times and previews taking more disk space. And if i share Photos to 30 users total size of all thumbnails folders can be more than size of Photos 
Is there any way to create thumbnails ones and give it to all users? i try to trick - create preview by my user, create in server symbolyc link from my thumbnails folder to thumbnails folder of another user, rescan all by occ. But it does not works 
Gallery looks very pretty, dont wont to disable it for economy diskspace…