Hello @katperf,
Thank you for reaching out to us!
We have to rule out theme or plugin incompatibility. Can you please deactivate all of your plugins except Strong Testimonials and see if it works afterwards?
If it does, turn them on one by one until you find a culprit.
If it still does not work please activate a default WordPress theme (Twenty Nineteen for example) and see if it works with that default theme.
Let me know what you find!
All the best,
Mihaela