Some published links are not working

Hi there everyone,
OJS version:
In a published issue, some articles links are broken. The pdf button loads the article just fine.
For exemple, this one is ok:
and this one is broken:
Any clues?

Hi @melise,

When I clicked on the link I got this error " 504 Gateway Time-out" - you might want to check with your website hosting/systems administrator (if that’s not you) about that error (you can read more here: 504 Gateway Timeout - HTTP | MDN) You also might want to check your PHP error log and report on any errors from there here on the post?

PKP Team

HI @rcgillis!

I found this fatal error:
PHP Fatal error: Empty reply from server in /var/www/html/lib/pkp/classes/webservice/ on line 228, referer: