Michael Gauland writes: > This is all the*trace-output* buffer shows: > > ====================================================================== > 1 -> (replace-buffer-contents #) > 1 <- replace-buffer-contents: nil Indeed, the `replace-buffer-contents` call is failing. I've been able to reproduce with earlier versions of emacs 26.1. With later versions of emacs 26, the problem goes away. It seems earlier versions of `replace-buffer-contents` are not quite reliable. It was patched prior to 27.1 and the new documentation string makes some guarantees of correctness, so let's just change the minimal version to 27.1. Thank you for the report. Regards, -- Sébastien Miquel X-Woof-Bug: confirmed