1) Yes, "singly" option is checked.
2) Yes, MaxBulk Mailer Pro is my version.
As a followup, I sent myself a "live" email, not a test, and the Tags were properly replaced with custom content. Hopefully that is my workaround solution.
Need troubleshooting for the Tag feature.
I insert Tags into Message. In the Preview mode, Tag is properly replaced by custom content from the Recipients page.
I send myself a Test email. When delivered, the email content displays the Tag name ("Opt 1") rather than the custom content desired...