You are probably right in that it is an issue with a configuration file or plugin. I’ve already turned off all non-critical plugins to no avail.
At this point I’ve decided not to use the add-on. It would be nice to use it, but adds unnecessary complexity to the site.
Thank you for your help:)
Dave:)
As a follow up, I ran a test on a production site. Instead of reusing an existing subscription email, I used a test email completely unknown to the production site. In that case, the email subscription was completely lost. There was no entry in the subscriber list. (as opposed to a subscription to every list.)
