Hello,
All you need to do is go to https://www.ads-software.com/download/ and download and extract only the two folders wp-admin and wp-includes to your website ftp and it will fix immediately.
This shouldn’t be related to ssl but rather a plugin you have that has wrong Group and owner permissions (https://helpdesk.ugent.be/img/wscp3014.gif). You can use winscp ftp or any other client to check if any plugin has wrong group and owner permission. When you find the plugin folder try to set it same as other folders group and owner.
Last step is to disable and re-enable that plugin. If you don’t do these steps you will keep getting http 500 error upon updating plugins, theme, or wp version. After all if this keeps showing up you can try to disable really simple ssl or other ssl plugin just for the sake for updating plugins or something.
Keep me updated!
