@mathpunk https://www.gnu.org/software/emacs/manual/html_node/elisp/Profiling.html

It’s best to capture a report of the slowdown with the profiler and submit to the maintainers of whatever project you’re using for development (I have a feeling I’ll be one of the people receiving that report). 😄

Be careful if you use spacemacs C-u reverts the buffer (with confirmation of course)