[O] Org mode fontification broken

[Peter Westlake]

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.