Describe the bug

There seems to be a regression in v3.13.8 vs v3.13.7 - exact same code in both cases:

// somewhere above
const measureElement: Parameters<typeof useVirtualizer>[0]["measureElement"] = (
  element,
) => element.getBoundingClientRect().height;

const estimateSize = () => 72;

const virtualizer = useVirtualizer({
  count: messages?.length || 0,
  getScrollElement: () => parentRef.current,
  estimateSize,
  measureElement,
  getItemKey: (index: number) =>
    messages?.[index] ? idExtractor(messages[index]) : nanoid(),
});

// somewhere below
const lastBeforeDateIndex = messages.length - 1; // this is a bit more complicated in the actual code, but most often resolves to this

// some other irrelevant logic, including a getVirtualItemForOffset call

virtualizer.scrollToIndex(Math.max(lastBeforeDateIndex, 0), {
  align: "start",
  behavior: "smooth",
});

For context, I have an infinite list in which items (messages) are occasionally appended. The items themselves have a dynamic size. When an item is appended, the list should be scrolled all the way to the bottom, so that the last item is visible.

Your minimal, reproducible example

/

Steps to reproduce

/

Expected behavior

3.13.8 retains the same behavior as 3.13.7

How often does this bug happen?

Every time

Screenshots or Videos

3.13.7 - scrolls correctly, bottom of last item is visible

3.13.8 - doesn't scroll correctly, last item is cut off

Platform

Brave on Linux, though it seems to reproduce everywhere

tanstack-virtual version

v3.13.8

TypeScript version

v5.8.3

Additional context

No response

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• I understand that if my bug cannot be reliable reproduced in a debuggable environment, it will probably not be fixed and this issue may even be closed.