Pretty hard to explain …
When you open your account page in a a web browser with pictures, apparently, server load a certain amount of files (photos and videos).
Now, you take the last updated picture uploaded on the server, you open it in large view and you click on the right arrow to the next picture, when you reach the last picture loaded by the server, you go back to the first picture.
Same behavior on list view and grid view.
Same on Firefox and Brave.
Debian 10 / 64 bits