When the profiler is present, the following JS error shows on every exception page:

To repeat:

composer create-project symfony/skeleton exception_js_error
cd exception_js
composer require twig profiler
php -S 127.0.0.1:8000 -t public

Then go to any error page, like http://localhost:8000/foo.

It appears that the Sfjs.createTabs() (that executes the createTabs() method in base_js.html.twig of the WebProfilerBundle) is called twice. The first time works, but the second time, some classes (which were removed the first time) are missing.

It's possible this came from 1c595fc#diff-de00cc2fe56e59a48a4d26e7a0dccca3, but I'm very not sure - maybe @ro0NL can prove/disprove my theory. Updated - it doesn't look like that specific change was the problem - as changing back has no effect. Sorry for the noise.

Cheers!