Your bug report

#43016: replace-region-contents takes a lot of time when called from json-pretty-print-buffer

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 43016@debbugs.gnu.org.

-- 
43016: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=43016
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