layout problem in expanding grid items at the right most side

Please see screenshot, when all the other grid items expansionedperfect except the last column on the rightmost side.

https://codepen.io/robertwong68/pen/rzJydV

Start with the linked CodePen reproduction and compare expansion behavior for the rightmost grid item with items in other columns. Inspect the Packery grid expansion and positioning entry points used by that example. Done means the last-column item expands and lays out consistently without the right-edge problem shown in the screenshots.

Written by the indexing model from the issue text.