Since a few days, before and after updating the plugins, my site has started showing an error on the frontend. I still have access to the WordPress admin area (wp-admin) with no errors, but any public-facing pages look all messed-up.
Please disable third-party plugins and customizations (if there are any) and check if this issue persists. If you use a caching plugin, make sure that caching is disabled for logged-in users. Also, if you see a critical error, I recommend checking your PHP logs, which usually contain more detailed information: How to configure WordPress error logs to identify and resolve problems - HivePress Help Center
I deactivated all plugins and then reactivated them 1 by 1. The website started working correctly again immediately but it lasted for 1 week and now I see the same problem again. This makes it even harder to narrowing down the search for the defected plugin. What can I do?
Please clarify what changes you made after disabling all third-party plugins (perhaps you have reactivated third-party plugins or added new third-party plugins, etc.). Also, please send a link to your website.