Unnumber chapters in the TOC are not shown as active with bookdown::gitbook - r-markdown

Question

I am currently writing a manuscript using Bookdown and the GitBook format.
My first and last chapters (Introduction and Conclusion) are unnumbered, whereas the 2nd and 3rd chapters are numbered.
However, when rendering the book and navigating throughout the different pages, the unnumbered chapters are never displayed as “active” in the Table of Contents (left-side bar).
Instead, the 1st numbered chapter (named "Chapter1" in the following code) is displayed as active (highlighted) when the current page is either the "Introduction" or "Conclusion".
When navigating to any numbered chapter ("Chapter1" or "Chapter2"), they are correctly displayed as active, as expected.
This can be verified by inspecting the elements in the TOC: the numbered chapters have the chapter class, and the 1st numbered chapter has both chapter and active when reading the unnumbered chapters. Unnumbered chapters do not have the chapter nor active classes.
I have tried adding the "chapter" class by using {- .chapter}, to no effect. Making all chapters numbered effectively makes the correct one displayed as active, but is not optimal (since I would like to use unnumbered chapters).
How can I make Bookdown correctly display the correct chapter as active, without making all of them numbered?
Here is the minimal example, the result is the same whether I put all code in the index.Rmd or in separated index.Rmd, 01-chap1.Rmd, 02-chap2.Rmd, ..., files.
Also, we can notice that using {-} or {.unnumbered} results in the same behaviour.
index.Rmd
---
title: "A Minimal Book Example"
author: "John Doe"
date: "`r Sys.Date()`"
site: bookdown::bookdown_site
output:
bookdown::gitbook: default
---
# Introduction {-}
Lorem ipsum
# Chapter1
## Section 1
# Chapter 2
## Section 1
# Conclusion {.unnumbered}
I also include an image to demonstrate the problem: we can clearly see that the current page is the "Introduction" chapter, however the highlighted ("active") chapter is "Chapter1".
Thank you in advance!

Answer 1

Try using the option to split by chapter.
In my experience it works as long as the chapters are not on the same HTML page.