Failed to reset cache for the instance (bad plugin)

Symptoms

Certain WP Toolkit operations fail with an error resembling the following:

CONFIG_TEXT: Scanning for WordPress websites was performed with errors:
Failed to register instance at '/home/user/public_html/wp-content/plugins/plugin-name/file.php': Failed to reset cache for the instance #XX: Error: Error establishing a database connection.

CONFIG_TEXT: Failed to reset cache for the instance #3: Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 10485760 bytes) in /home/user/public_html/wp-content/plugins/plugin-name/file.php on line XX

CONFIG_TEXT: Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 10485760 bytes) in /usr/local/cpanel/3rdparty/wp-toolkit/plib/vendor/wp-cli/vendor/wp-cli/php-cli-tools/lib/cli/Colors.php on line 21

Cause

Errors with plugins can cause the command-line operations of WP Toolkit to fail. This prevents WP Toolkit from operating properly with the blog, leading to several issues, including failing to add a new instance or failing to perform an update.

Resolution

Disabling the plugin will often resolve the error. If the blog is already registered with WP Toolkit, you can try to disable the plugin using the tools there:

How to enable or disable WordPress plugins in WP Toolkit

Otherwise, you may need to disable the plugin manually through the default WordPress administration panel. The logged errors will often tell you which plugin is causing the error, but you can enable WP Toolkit extended logging to gather more information if necessary:

How To Enable Enhanced Logging In WP Toolkit?