This is a true story of being a developer:
For the better part of the day I’ve been trying t track down why twig debug wasn't working on one of my dev environments.. Now, generally speaking, turning on twig debugging is simple: Change a flag in your services.yml, clear your Drupal cache, and rock and roll. I’ve done this 100’s of times, so, why today isn’t this working?
I start to think about it, the only thing non-traditional about the way I handle this is that I have a separate services.yml set up for my dev environment (dev.services.yml) and test for what environment I'm in in settings.php and load the appropriate services file. This has worked for years but just to be sure, I use drush to tell me the status of the debug flag and it's fine
So I. know the right services file is loading. I check multiple browsers, make sure the comments are turned on in the browsers' page source tool. I make sure Drupal caching is turned off. I start googling, and am getting no where. Spent some time spinning down rabbit holes, disabling browser plugins, reading Drupal Core source and really got no where. I stepped away, went for a walk. Sat down to work on something else and then....
It Hit Me! Last week, I was debugging a problem which required me to turn on Cloydflare's caching against this environment, something I never do. Cloudfare's HTML compression was also turned on which stripped out the comments, so debug messages weren't being seen.So I flipped Cloudflare to DNSonly for this sub-domain, wait 15 mins for DNS to propagate, cleared Drupal cache, and it worked. It's always the simple things.