Also, so you all know:
I have a feeling the CSRF Token issue is related to the "LDAP Authentication and Lookup" plugin we are using. I redownloaded the phar file for this plugin from the osTicket website (thinking maybe there was a new version) and replaced the one we have installed. Unfortunately, we had another short spat of CSRF Token errors in the System Logs.
Finally, I spoke to Google technical support about this just to see if there could be anything on their end causing these mailer issues. They looked at everything - including the mail settings setup in osTicket. Unfortunately, they concluded that there isn't anything on their end causing the issues.