Five failure patterns from past WordPress major upgrades — what 5.0 Gutenberg through 6.0 FSE taught maintenance teams

Short summary

This article catalogs five recurring failure patterns from WordPress major upgrades (5.0 through 6.0): editor-adjacent plugin breakage from Gutenberg, silent jQuery 3.x runtime failures, PHP version incompatibilities deactivating plugins, Classic-to-Block Theme migration gaps, and delayed REST API auth failures in external integrations. Each pattern includes root cause analysis and concrete fix patterns such as compatibility layers, staging soaks, and pre-upgrade dependency inventories. The structural lessons generalize to future major releases, helping maintenance teams triage faster when 7.0 or 8.0 lands.

• •Gutenberg (5.0) broke TinyMCE-dependent meta boxes and plugin editor extensions — fix with Classic Editor plugin bridge and pre-upgrade dependency inventory
• •jQuery 1.x to 3.x (5.6) caused silent front-end JS failures — fix with jquery-migrate compatibility layer and console-driven staging verification
• •PHP version jumps deactivate plugins or white-screen sites — test plugins against new PHP before upgrading and evaluate replacements for stale 'Tested up to' values
• •FSE (6.0) invalidated Classic Theme child-theme overrides when switching to Block Themes — treat theme migration and WordPress upgrade as separate decisions
• •REST API auth and scope changes break external integrations days or weeks post-upgrade — use one-week staging soaks and end-to-end integration testing

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