It was also happening pre 4.4 and disabling the plugin fixes the issue, so I feel it’s very much a Yoast problem…
A follow up on this…. I enabled WordPress debug but didn’t have any new errors. I have exact clone on our live site on a smaller server and migrated the live site to this staging site and weirdly the plugin works fine and doesn’t effect any of the admin pages.
Surely the larger server for our live site would run the plugin better? I’ve contacted our hosting supplier to get them to have a look and I’ll update here when I get an answer.
