Liquid Syntax error

[KnorrFG]

Hey,
when I try to use jekyll-email-protect and I run bundle exec jekyll serve, I get the warning:
Liquid Warning: Liquid syntax error (line 19): Unexpected character @ in "{{ [email protected] | encode_email }}" in about.md, and the link on the generated page is just "mailto:"

I tried adding jekyll-email-protext in the _config.yml via gems, which yielded a deprication warning, and via plugins, which did not yield a warning, but still the error.

In my gemfile I tried adding the gem in the jekyll-plugins group and outside of it. Didn't make a difference.

When I run
bundle exec gem list --local | grep protect
jekyll-email-protect is found, and when I run jekyll doctor it says everything looks fine.

I'm running Ubuntu 18.04 and Ruby 2.5.1p57