Problem solved! I had forgotten that I was using a copy of the Org repository instead of the package bundled with Emacs.
Peter. On Mon, 12 Nov 2018, at 14:52, Peter Westlake wrote: > Since upgrading from Fedora 27 to Fedora 28, Emacs 26.1-3.fc28.x86_64, > links and other fontified text in Org files appear as the underlying > plain text. A few of them look correct, and deleting a marker character > (e.g. square bracket) and reinserting it makes the link appear correctly > for a while. The Messages buffer is full of things like this: > > Error during redisplay: (jit-lock-function 501) signaled (wrong-type- > argument listp org-level-4) > Error during redisplay: (jit-lock-function 1001) signaled (wrong-type- > argument listp org-level-4) > Error during redisplay: (jit-lock-function 1501) signaled (wrong-type- > argument listp org-level-3) > Error during redisplay: (jit-lock-function 2001) signaled (wrong-type- > argument listp org-level-3) > Error during redisplay: (jit-lock-function 1152403) signaled (wrong- > type-argument listp org-level-2) > > I've attempted to set jit-lock-mode to nil in .emacs, with no success. > > This Emacs has a built-in version of Org, 9.1.14, and I've tried > 20181125 installed through Melpa. Nothing makes a difference. > > Any ideas? > > Peter. >