This image from https://drive.google.com/file/d/1W0A2E2GIwi6mq9b94FzA7PhfXCae-VPB/view originally created by Daniel Rudansky
The pattern appears to build up, adding dots and colors, leaving the sequence "full" at the fifth square, with no room to add anything after that, so you could make an arbitrary choice as to what happens next, such as:
The sequence repeats, so the sixth square looks just like the first square. Or the sequence resets before it repeats, and the sixth square is empty. Or the sequence follows the pattern ABCDEDCBA, and the sixth square looks like the fourth square.
If we take this pattern as a part of a bigger and complete pattern with a well defined rule, then this makes sense:
It is a complete palindrome-like pattern with "mirrored" operations (add-change-add- change-change-remove-change-remove). It eliminates the obscurity how to add white spheres after item 5. It involves operations that have already been used, so in this sense it is not arbitrary any more.