WordPress Recurring 500/503 Errors, Fatal Theme Bug, Slow Queries (Custom Theme + Events Calendar)

Our WordPress site (Cloudways-hosted, custom theme "mangala-shri-bhuti," running WooCommerce + The Events Calendar) has had a pattern of recurring instability over the past several days — different specific errors each time, but a consistent shape: slow Events Calendar queries, PHP worker exhaustion, and now a fatal PHP error, together causing intermittent outages for both site visitors and backend/admin users. What we know so far (from our host's diagnostics and our own investigation): A fatal PHP error in our custom theme, header-dharma-post-meta-info.php line 6 — appears to loop over post taxonomy terms without handling the case where get_the_terms() returns false (no terms assigned). Currently causing ~50% of page loads to fail with HTTP 500. The Events Calendar plugin's date-filtered/paginated pages are taking 150-255 seconds to load, tying up PHP workers and contributing to server-wide slowdowns (load average 26-43 on a 4-core server). Our PHP-FPM configuration allows up to 40 concurrent workers × 2GB memory each (80GB theoretical) against only 8GB of actual server RAM — a mismatch that has previously caused repeated out-of-memory crashes. We enabled Redis at the server level, but WordPress may not yet be fully using it as a persistent object cache — needs verification. We identified and blocked two bot IPs that were aggressively crawling paginated event-archive URLs, which had been a contributing traffic trigger. A cosmetic PHP warning in Elementor (dynamic-tags) has also appeared in logs but is confirmed unrelated to the outages. What we need: someone who can look at this holistically rather than just patch the latest reported error — diagnose whether these are one root cause manifesting differently under load, or several distinct issues, fix the theme bug, resolve or substantially improve the Events Calendar query performance, correct the PHP worker/memory configuration, and confirm the object cache is actually functioning. We can provide full hosting diagnostic reports, server access, and everything we've investigated so far. Deliverables: Fatal theme error fixed and verified (including for posts/admin views with no assigned topic) Events Calendar date-filtered pages loading in a reasonable time PHP-FPM worker/memory settings corrected to match actual server resources Object cache confirmed active and functioning (via WordPress Site Health) Brief written report: root cause(s) identified, what was changed, and any remaining risk