Adding Jekyll collections prevent posts from rendering - jekyll

Question

I have a strange problem where adding collections and collections_dir allows me to get one result where I can view the collection results on the ML Projects page that you can see in the sidebar of my website but it prevents any posts in _posts from rendering.
After doing some research I learned that posts is a collection by default, but I'm not sure how this helps me. I tried moving the _posts directory into the _projects directory, which is my collections_dir, but that does not work.
To replicate issue:
Clone the repo at https://github.com/luke-anglin/lukes_site
Build and serve the site, noting that posts do render
Go to _config.yml and remove the comments on line 26-29 which specify the collection and the collections_dir
Rebuild and see that the posts disappear, but the collection things work.
config.yml
# Dependencies
markdown: kramdown
# Permalinks
permalink: pretty
# Setup
title: Luke Anglin
tagline: Computer Science and Engineering Student
description: Software Engineering, DevOps, Data Science
url: http://localhost:4000/
baseurl: /
author:
name: Luke Anglin
# url: https://twitter.com/mdo
plugins:
- jekyll-paginate
paginate: 5
paginate_path: 'page:num'
# Custom vars
# Collections
# collections:
# - ml
# collections_dir: _projects
version: 2.1.0
github:
repo: https://github.com/luke-anglin/lukes_site
defaults:
- scope:
path: 'static/assets/media'
values:
image: true
index.html where the posts are supposed to be looped through
---
layout: default
title: Home
---
<div class="posts">
{% for post in paginator.posts %}
<div class="post">
<h1 class="post-title">
<a href="{{ post.url }}">
{{ post.title }}
</a>
</h1>
<span class="post-date">{{ post.date | date_to_string }}</span>
{{ post.content }}
</div>
{% endfor %}
</div>
<div class="pagination">
{% if paginator.next_page %}
<a class="pagination-item older" href="{{ site.baseurl }}page{{paginator.next_page}}">Older</a>
{% else %}
<span class="pagination-item older">Older</span>
{% endif %}
{% if paginator.previous_page %}
{% if paginator.page == 2 %}
<a class="pagination-item newer" href="{{ site.baseurl }}">Newer</a>
{% else %}
<a class="pagination-item newer" href="{{ site.baseurl }}page{{paginator.previous_page}}">Newer</a>
{% endif %}
{% else %}
<span class="pagination-item newer">Newer</span>
{% endif %}
</div>
Any other info can be found in the repo. Let me know if there are any other questions.

Answer 1

Try to remove the leading '_' from '_projects' directory. The 'collections_dir:' isn't allowed to have this character in the name of the target folder.
See: https://jekyllrb.com/docs/collections/
Particularly the red notice labeled 'Be sure to move drafts and posts into custom collections directory'. At the end it mentions 'Note that, the name of your collections directory cannot start with an underscore (_).'
Hope this helps.