Problems after updating to WordPress 5.x

Historical note: this guide refers to the jump from WordPress 4.x to 5.x. For a current installation, use compatible, maintained versions of WordPress, PHP, themes and plugins.

A failure appearing after an update does not on its own prove that WordPress or a plugin is the cause. Reproduce the symptom once and check the error logged at that same moment.

Diagnosis

1. Make a backup before changing any components.
2. Reproduce the action that fails and note the time and the URL.
3. In WordPress 5.2 or later, also check the recovery email; earlier versions do not have this feature. Check the PHP log. If you do not have one, temporarily enable the private debug log.
4. Note the first fatal error of the request, including the file, the line and the component mentioned.

A file inside wp-content/plugins/ or wp-content/themes/ identifies the component that was running, but you still need to check whether it is out of date, whether there is a documented incompatibility or whether it received invalid data from another component.

Apply the narrowest fix

• Update the indicated component first and check its WordPress and PHP requirements.
• If you cannot get into wp-admin, use recovery mode. As a reversible measure, you can rename only the folder of the identified plugin and reload the same URL.
• If the log does not point to a component, reproduce the problem on staging and run a conflict test: temporarily switch to a default theme and disable plugins in groups.

A test only confirms the link if the same action fails with the component active and works when you disable it. Then restore the original configuration and look for an update or a fix from the vendor.

Also check Site Health to spot unmet requirements, but do not treat every recommendation as the cause of the failure.

Editor changes and old content

The jump to WordPress 5 introduced the block editor, but an interface change is not the same as a PHP error. If the problem happens when editing a post, keep a revision, check the Console and Network tabs and review the compatibility of the theme and plugins with the editor you use.

Do not bulk-convert old content or downgrade the core to fix a single screen. Test a representative copy first, keep its revisions and check that the public content keeps its design, links and images after the change.