Fix Unknown WordPress Plugin Conflict

My WordPress site suddenly broke due to a plugin conflict. I’m not sure which extension is responsible and the issue didn’t follow any obvious change, so I can’t trace it to a recent install or update. Right now pages either fail to load or behave unpredictably whenever plugins are active, while the theme files themselves seem unaffected.

I need someone who can:
• Quickly pinpoint the offending plugin without disabling essential functionality for long periods.
• Restore full site stability and ensure all core features, theme customisations and existing plugins play nicely together.
• Give me a brief summary of what went wrong and how you fixed it so I can prevent a repeat.

This is a small‐scale job with a tight budget, so efficient troubleshooting is critical. If you’re comfortable with WordPress debug tools, error logs, and safe staging environments, I’d love your help.