Ok, I’ve looked into this further and I was wrong about script debugging resolving the issue. Not sure why it seemed to fix the issue at first, but it’s back again now and adding/removing the debug line in wp-config.php makes no difference.
I am accessing the WordPress admin via a local server. When I access the admin directly via MAMP as the local server, there are no problems, but when I access via Mixture as the local server, the problem occurs. I think it’s something to do with how Mixture’s local server handles processing of javascript, possibly along the lines of this comment on another similar post:
https://support.mixture.io/discussions/problems/4572/r?go=aHR0cDovL3dvcmRwcmVzcy5vcmcvc3VwcG9ydC90b3BpYy9mcmVzaC0zNjEtaW5zdGFsbC12aXN1YWwtZWRpdG9yLWFkZC1tZWRpYS1ub3Qtd29ya2luZy13aGl0ZS10ZXh0P3JlcGxpZXM9OSNwb3N0LTQ2NzUwOTE=
For now, I’ll just use MAMP!
