I found the issue. My NSE was calling the contentHandler twice at some point which is why it couldn't be updated anymore.

Yes, I actually have used that you can see I still have a function called preCacheImages unless I did do something wrong, it doesn't change the memory usage... Additionally I don't know a way to see which rows are "coming up"... or should I just load all photos at once (that doesn't seem like the correct way of doing it.)

I have, however that would make it one more step for the user. Because I want to have a grid view and on top of that is a square where the user can move and zoom the selected photo from the grid within the same view. (This part is missing in above code)