Rails: Byebug doesn't print in console

Question

From some unknown reasons, Byebug stops printing code in console.

For example, I've added byebug in following test:

What I've got in console / terminal:

Do you have any idea what could be wrong or where could I search for a reason of this problem?

EDIT:

Command how I run tests:

$ rake spec

EDIT 2:

When I run server with Byebug in any place it also doesn't work. It even doesn't print any logs. This is how does it look console after running server and sending to them some requests - ... empty:

That does it doesn't print in console could be caused by puma.rb configuration:

min_threads_count = ENV.fetch('RAILS_MIN_THREADS') { 5 }.to_i
max_threads_count = ENV.fetch('RAILS_MAX_THREADS') { 5 }.to_i
threads min_threads_count, max_threads_count

bind "unix:///var/run/puma.sock?umask=0000"

stdout_redirect "/var/log/puma.stdout.log", "/var/log/puma.stderr.log", true

environment ENV.fetch('RAILS_ENV') { 'development' }

plugin :tmp_restart