I can't upload more than 12 photos from the Android photo app to my NC-server

I can’t upload more than 12 photos from the Android photo app to my NC-server (14.0.3).
I have selected 22 photos from the Android photo app and used the share feature to upload them to my NC-server but it never uploads more than 12 photos.
I did some investigation on the web for this problem but couldn’t find a resolution so far.
Some people a saying that this has to with Google Pixel 2 XL and Android 9 but I have just tried to do the exact some thing but I uploaded/shared my photos to my Google Drive and that worked just fine. Has anybody experienced the some problem? Is anybody aware of a fix?