[Bug]: bundle exec jekyll serve command does not see _plugins directory

Operating System

macOS Tahoe

Ruby Version

ruby 3.4.9 (2026-03-11 revision 76cca827ab) +PRISM [aarch64-linux]

Jekyll Version

jekyll 4.4.1

GitHub Pages Version

No response

Expected Behavior

I expect my site to be served up locally, with working plugins from the _plugins directory.

Current Behavior

Preface: Everything executes in a docker container, via bundle exec. If I execute:

bundle exec jekyll serve --force_polling --host 0.0.0.0 -p 4000 --watch --config=_config.yml,_config_development.yml

Plugins are not found, and plugin use results in a crash with traceback

If, instead, I use:

bundle exec jekyll serve –-plugins _plugins --force_polling --host 0.0.0.0 -p 4000 --watch --config=_config.yml,_config_development.yml

Everything works fine. If I execute jekyll build (same container, same volumes, etc.) and no --plugins option, the site is generated correctly as well.

I have verified that the _plugins directory is present within the /site directory, as evidenced by it working when I explicitly specify it and by the build command working correctly as well, without it.

Relevant log output

▶ Preparing local site (watched)...
Installing bundle (possibly from cache)...
Validating configuration...
Using      : jekyll 4.4.1
Environment: JEKYLL_ENV=development
Exec       : jekyll serve --force_polling --host 0.0.0.0 -p 4000 --watch --trace --config=_config.yml,_config_development.yml
Configuration file: /site/_config.yml
Configuration file: /site/_config_development.yml
 Theme Config file: /Users/dolf/Documents/Dolf-Sites/jekyll-sites/extra/jekyll-theme-chirpy/_config.yml
            Source: /site
       Destination: /site/_site
 Incremental build: disabled. Enable with --incremental
      Generating... 
  Liquid Exception: Liquid syntax error (line 5): Unknown tag 'items' in /site/_posts/2025-06-10-on-our-way.md
bundler: failed to load command: jekyll (/usr/local/bundle/ruby/3.4.0/bin/jekyll)
/usr/local/bundle/ruby/3.4.0/gems/liquid-4.0.4/lib/liquid/document.rb:23:in 'Liquid::Document#unknown_tag': Liquid syntax error (line 5): Unknown tag 'items' (Liquid::SyntaxError)
	from /usr/local/bundle/ruby/3.4.0/gems/liquid-4.0.4/lib/liquid/document.rb:11:in 'block in Liquid::Document#parse'
	from /usr/local/bundle/ruby/3.4.0/gems/liquid-4.0.4/lib/liquid/block_body.rb:32:in 'Liquid::BlockBody#parse'
	from /usr/local/bundle/ruby/3.4.0/gems/liquid-4.0.4/lib/liquid/document.rb:10:in 'Liquid::Document#parse'
	from /usr/local/bundle/ruby/3.4.0/gems/liquid-4.0.4/lib/liquid/document.rb:5:in 'Liquid::Document.parse'
	from /usr/local/bundle/ruby/3.4.0/gems/liquid-4.0.4/lib/liquid/template.rb:130:in 'Liquid::Template#parse'
	from /usr/local/bundle/ruby/3.4.0/gems/liquid-4.0.4/lib/liquid/template.rb:114:in 'Liquid::Template.parse'
	from /usr/local/bundle/ruby/3.4.0/gems/jekyll-4.4.1/lib/jekyll/liquid_renderer/file.rb:13:in 'block in Jekyll::LiquidRenderer::File#parse'
	from /usr/local/bundle/ruby/3.4.0/gems/jekyll-4.4.1/lib/jekyll/liquid_renderer/file.rb:70:in 'Jekyll::LiquidRenderer::File#measure_time'
	from /usr/local/bundle/ruby/3.4.0/gems/jekyll-4.4.1/lib/jekyll/liquid_renderer/file.rb:12:in 'Jekyll::LiquidRenderer::File#parse'
	from /usr/local/bundle/ruby/3.4.0/gems/jekyll-4.4.1/lib/jekyll/renderer.rb:124:in 'Jekyll::Renderer#render_liquid'
	from /usr/local/bundle/ruby/3.4.0/gems/jekyll-4.4.1/lib/jekyll/renderer.rb:80:in 'Jekyll::Renderer#render_document'
	from /usr/local/bundle/ruby/3.4.0/gems/jekyll-4.4.1/lib/jekyll/renderer.rb:63:in 'Jekyll::Renderer#run'

... ABBREVIATED

Code Sample

The docker file used, and its entrypoint script can be found in the docker directory here: https://github.com/dolfs/jackal