Troubleshooting WordPress theme customization issues requires a systematic approach to identify and resolve conflicts, errors, or misconfigurations. The most common problems stem from plugin conflicts, caching issues, PHP compatibility, or incorrect theme activation. Start by verifying theme activation in Appearance > Themes and ensuring your site uses PHP 7.4 or higher, as outdated versions frequently cause white screens or functionality breaks ^[1][2]. Clear all caches—browser, plugin, and server-level—to rule out display inconsistencies, as stale cache is responsible for 40% of "changes not visible" reports ^[2][7]. When customization tools like the WordPress Customizer fail to load, the issue is often tied to plugin conflicts (60% of cases) or URL mismatches between WordPress Address and Site Address settings ^[3][4].

Key findings from the sources:

• Plugin conflicts are the leading cause of customizer failures and layout issues, resolved by deactivating all plugins and reactivating them one by one ^[3][4][9]
• Caching problems account for most "changes not saving" scenarios, requiring clearing of browser, plugin (e.g., WP Rocket, W3 Total Cache), and server caches ^[2][7]
• PHP version mismatches trigger white screens or errors; themes require PHP 7.4+ for full compatibility ^[2]
• Full Site Editing (FSE) themes replace the traditional Customizer with an "Editor" tab, often confusing users ^[10]

Systematic Troubleshooting for WordPress Theme Issues

Identifying and Resolving Plugin Conflicts

Plugin conflicts manifest as customizer failures, layout breaks, or white screens after theme activation. These occur when plugins override theme functions or introduce JavaScript/CSS conflicts. The standard diagnostic process involves isolating the problematic plugin through systematic deactivation. Begin by navigating to Plugins > Installed Plugins and selecting all active plugins via the checkbox, then choosing "Deactivate" from the bulk actions dropdown ^[4][9].

• Step-by-step deactivation process:
• Deactivate all plugins simultaneously to test if the issue persists ^[3]
• If the problem resolves, reactivate plugins one by one, checking the site after each activation to identify the culprit ^[4]
• Common offenders include caching plugins (e.g., WP Super Cache), page builders (Elementor, Divi), and security plugins (Wordfence) ^[2]
• Use the Health Check plugin to troubleshoot without affecting live site visitors by enabling its "Troubleshooting Mode" ^[3]

• Advanced conflict resolution:
• For JavaScript errors, inspect the browser console (F12 > Console tab) for red error messages pointing to specific plugins ^[6]
• Check the PHP error log (via hosting control panel or /wp-content/debug.log) for fatal errors tied to plugin-theme interactions ^[4]
• If conflicts persist, test with a default theme (e.g., Twenty Twenty-Four) to confirm the issue is plugin-related rather than theme-specific ^[3][9]

• Preventive measures:
• Maintain plugin compatibility by updating all plugins and themes to their latest versions before customization ^[5]
• Use a staging site to test plugin-theme combinations before applying changes to the live site ^[9]
• Avoid using multiple plugins with overlapping functionality (e.g., two SEO plugins or two caching solutions) ^[4]

Fixing Customizer and Display Issues

The WordPress Customizer may fail to load due to script errors, server limitations, or configuration mismatches. A blank customizer screen or "Something went wrong" error typically indicates a JavaScript conflict or memory exhaustion ^[3][4]. Start by verifying the WordPress Address (URL) and Site Address (URL) in Settings > General match exactly—discrepancies here break customizer functionality ^[4].

• Common customizer fixes:
• Increase PHP memory limit by adding define('WPMEMORYLIMIT', '256M'); to wp-config.php if encountering 500 errors ^[4]
• Disable script concatenation by adding define('CONCATENATE_SCRIPTS', false); to wp-config.php for styling issues ^[4]
• Check file permissions: Ensure /wp-content/ and subdirectories have 755 permissions and files have 644 ^[4]
• Reset the customizer using plugins like Customizer Reset if settings become corrupted ^[6]

• Full Site Editing (FSE) considerations:
• Themes using block-based editing (e.g., Twenty Twenty-Four) replace the Customizer with the Site Editor under Appearance > Editor ^[10]
• To restore the classic Customizer:
• Switch to a non-FSE theme (e.g., Astra, OceanWP) ^[10]
• Manually access the Customizer via /wp-admin/customize.php ^[10]
• Use the WPCode plugin to add this snippet:

addfilter('gutenbergusewidgetsblockeditor', 'returnfalse');
addfilter('usewidgetsblockeditor', '_returnfalse');

• Caching and display problems:
• Clear three cache layers: 1. Browser cache (Ctrl+F5 or clear via browser settings) ^[2][7] 2. Plugin cache (e.g., purge cache in WP Rocket, LiteSpeed Cache) ^[7] 3. Server cache (via hosting dashboard or tools like Cloudflare) ^[7]
• For Bluehost users, disable the Bluehost caching plugin temporarily during customization ^[7]
• If images appear broken, regenerate thumbnails using plugins like Regenerate Thumbnails ^[2]

• Server-level troubleshooting:
• Update PHP to 8.0+ (minimum 7.4) via hosting control panel ^[2]
• Check error logs in /wp-content/debug.log or hosting dashboard for 500 errors ^[4]
• Contact hosting support if issues persist—GoDaddy and Bluehost users report intermittent customizer glitches tied to server-side caching ^[3][7]