When you're locked out, disable plugins through cPanel's File Manager.
- Log in to cPanel and open File Manager.
- Go to your WordPress folder, then
wp-content. - Rename the
pluginsfolder to something likeplugins-off. This deactivates every plugin at once. - Try logging in to
yourdomain.com/wp-adminagain.
Once you're back in, rename the folder back to plugins. Your plugins will appear deactivated; reactivate them one at a time from Plugins, reloading the site after each, until the broken one reveals itself. You can also rename a single plugin's subfolder to disable just that plugin. Still locked out after this? Open a ticket.