Hello. I do this on MacOS with Safari browser:
1) create album in group (save it with title)
2) drug and drop few photos and wait for upload finish
3) press on “star icon” to make few photos featured (usually I feature/unfeature photos to find best way to display it)
4) press on thumb
Result: photo doesn’t open in popup. Need to refresh page and try again (photo will be opened in popup).

I’m not sure if steps 3 and 4 are nessesary.

Thanks.