Keep items on theirs respective lanes when scrolling up on masonry

[juanabal]

I’m rendering dynamically sized items inside a masonry-style virtualized list. The main issue occurs when scrolling upward: items begin to render outside the viewport, and the layout shifts significantly. Keep in mind that these are items that were previously rendered, im not appending new items.

It appears that the virtualizer is attempting to keep the columns aligned while recalculating item positions, which results in noticeable layout instability. This causes the content to move unexpectedly during upward scrolling, making the experience quite disruptive and difficult to use.