The cause was likely the update to Connections which I released on Friday for a few hours.
Part of the issue is the server is very likely running a very old and unsupported version (for years). I recommend to update your site to run a more recent version of PHP. WordPress recommends version 7.0 due to it being much faster and far more resource efficient. I recommend at least version 5.6 (which is actually going to be unsupported soon if I remember correctly).
I did rollback the update after only a few hours so you must have been one of the few hundred who updated when this issue came to light…
You should be able to delete the
../wp-content/plugins/connections/ folder via FTP. The will let you back in you admin. Now you can reinstall Connections as you normally would. You data is completely safe and will not be deleted by deleting the plugin folder.
I will be releasing a revised update today which will make it work again on the very old version of PHP. It’s a very minor change but necessary for that old version. So you could also wait and install the new update if you wish.
My do apologize for the trouble this has caused you!