Poor performance but only on the scroll thumb

Describe the bug

The scroll thumb consistently has incredibly bad performance on large, dynamic lists. This is pretty pervasive in my platform which uses tanstack/virtual quite a lot. More pronounced in development but still quite noticeable in production. sort of seems disconnected from real life render performance too?

Your minimal, reproducible example

Hard to repro without pretty large real life example

Steps to reproduce

use tanstack/virtual with a large list of complex items

Expected behavior

I expect the thumb to perform natively. I wonder if the scroll event is getting blocked somehow?

How often does this bug happen?

Often

Screenshots or Videos

No response

Platform

https://github.com/user-attachments/assets/7839e896-7545-404b-957a-2a2a701e0134

tanstack-virtual version

3.13.12

TypeScript version

No response

Additional context

No response

Terms & Code of Conduct

• I agree to follow this project's Code of Conduct
• 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.

No source file or test is named. Start by building a large list of complex, dynamic items with tanstack/virtual 3.13.12 and profiling scroll-thumb behavior in development and production. Done means a reliable reproduction and a verified performance improvement without regressing list rendering.