Please make a full backup of your site (files and database) and confirm it in your next reply.
If possible please provide access to the staging website, not production.
Please note, that I might need to do some debugging procedures like enable/disable plugins, switch themes, change the default language of the user account, and/or access your website database to debug the issue furtherly.
I would need to access both your site's wp-admin and FTP account.
I have enabled the private username and password fields in your next reply.
You can safely add your information into these fields.