How do you find which plugin or theme is causing the conflict?

We bisect. On a staging clone we disable all plugins, confirm the error clears, then re-enable them in batches until the culprit reappears, switching to a default theme to rule the theme in or out. This finds the single offending component fast without guessing. Once isolated, we patch it, roll it back, or swap it for a maintained alternative, we don’t leave half your plugins disabled.