WordPress (Windows Server) Expert Needed to Resolve Customizer Errors

I need a senior freelancer who is highly proficient in WordPress themes/plugins and highly proficient with Windows Server (IIS, FastCGI, PHP on Windows—not Linux). A newly installed theme is largely working, but the Customizer throws repeated warnings at the top of the page. The page eventually loads beneath the warnings, but we need a clean, robust fix that works with PHP 8.x and WordPress 6.8.x. After resolving this, I want the site reviewed for stability/performance on Windows Server and prepared for a smooth move to production.
The Issue
When clicking Appearance → Customize, multiple warnings appear repeatedly (page still loads underneath):
Warning: Attempt to read property "post_status" on null in C:\Websites\site\wp-admin\includes\template.php on line 2298
Warning: Attempt to read property "post_status" on null in C:\Websites\site\wp-admin\includes\template.php on line 2302
Warning: Attempt to read property "post_status" on null in C:\Websites\site\wp-admin\includes\template.php on line 2308
... (similar lines continue through ~2334)
What I suspect: a theme (or plugin) callback is being invoked during the Customizer load and assumes a valid global $post (e.g., reading post_status/ID) when in the Customizer there may be no current post (so $post is null). PHP 8+ elevates these to warnings that surface prominently. I need a developer who can pinpoint the offending code and implement a proper fix (guards/conditional logic, correct hooks, or updated logic) without modifying WordPress core.
Required Skills
WordPress (themes, child themes, hooks/actions, Customizer API, admin context vs. front-end)
Deep PHP 8.x compatibility work (null checks, deprecations, strict types behavior)
Windows Server + IIS: FastCGI, application pools, handler mappings, web.config, URL Rewrite
PHP on Windows: php.ini tuning, OPcache, error logging paths
MySQL on Windows: basic tuning, connection handling
Debugging with WP_DEBUG_LOG, stack traces, and isolating theme/plugin conflicts
Nice-to-Have
Experience hardening and optimizing WordPress on IIS (cache strategy, output buffering, object cache, FastCGI settings)
Familiarity with moving sites from localhost/staging to production on Windows
Scope of Work / Deliverables
Diagnosis & Root Cause
Review wp-content/debug.log and any IIS/PHP logs.
Identify the specific theme or plugin code causing Customizer to reference $post when null (common culprits: global $post usage, meta-box routines, direct calls to admin template helpers).
Provide a brief written root-cause summary.
Code-Level Fix (No Core Hacks)
Implement safe guards and correct hook placement (e.g., ensure Customizer paths don’t call post-edit routines; add $post instanceof WP_Post checks).
Ensure no changes to wp-admin/includes/template.php (core must remain untouched).
Confirm Customizer opens cleanly with zero warnings.
Compatibility & Regression Testing
Verify with the active theme and key plugins.
Confirm front-end and wp-admin critical paths work (login, menus, widgets/blocks, forms).
Confirm behavior on PHP 8.x and WordPress 6.8.x.
Windows-Specific Review
Check IIS FastCGI mapping to PHP, sensible InstanceMaxRequests/timeouts, and OPcache enabled.
Confirm WP_DEBUG_DISPLAY is off in production and logs route to the right location.
Sanity-check web.config rewrite rules for WordPress permalinks.
Brief recommendations for performance and stability on Windows.
Handover & Production Plan
Short write-up: what changed, where, and why.
Recommended steps to move from localhost to production on Windows Server (IIS app pool, DNS, SSL, permalinks flush, cache warm-up).
Optional: quick checklist for future updates.
Acceptance Criteria
Opening Appearance → Customize shows no PHP warnings/notices (with WP_DEBUG_DISPLAY disabled and WP_DEBUG_LOG enabled).
No edits to WordPress core files.
Site functions normally (front-end and admin).
Site loads fast
Brief documentation of the fix and any theme/plugin files touched.
Windows/IIS configuration remains stable and performant.
What I Will Provide
RDP or secure access to the localhost Windows Server environment (IIS) or zipped project as needed.
WordPress admin credentials for staging.
Recent logs (wp-content/debug.log) if helpful.
Theme/plugin list and any custom code locations if known.
Please Include in Your Proposal
A short plan for how you will identify and fix the Customizer warnings (tools, steps, expected touch points).
Your experience with WordPress on Windows Server/IIS (not Linux).
Estimated timeline.
Any additional suggestions you have for Windows-specific optimization or production cutover.