How to troubleshoot a run once code snippet

I am trying to troubleshoot a run-once code snippet that does not appear to be executing.
I have added define( ‘WP_DEBUG’, true); to the wp-config.php file.
I have tried inactivating and reactivating the Code Snippets plugin.
I have tried inactivting all plugins on the site.
I have tried using a mu-plugin with a logging function to see if it is running.
QM monitor is not reporting any errors
QM monitor is not recording any logging when I add a code to log a message.

Any other suggestions?

Thanks in advance,

bob