Visual Editor and other links blank in 2.8.4 new install

I seem to have re-created a problem that was occurring when 2.8 came out. I’ve just done a new install for a second domain within a subdirectory in public_html. I think this is the correct way to do it, and I can see and manipulate the site fine.
The problem is that the links and commands in Visual Editor and QuickPress are either blank or question marks.

The problem appeared with a fresh install – no additional plugs-in.

I’ve tried putting
define( ‘CONCATENATE_SCRIPTS’, false );
into the config_php file to no avail. I put it in line 2 after the asterisk, and also tried adding a line after line 2 and putting it there, though I didn’t think that would make a difference. It didn’t.

I’ve emptied my Safari cache after each change.

I’ve reloaded WP_includes.

The thing is, my main site, https://tribeofadmins.com, which is running the same version of WP, doesn’t have this problem. It’s the second domain I added: https://www.jewellyfish.com that is having the issue. I suspect it’s to do with how I installed it, but I don’t get what the problem is.

Help appreciated!