I experienced the same problem initially, where by it appeared that subscribers were not being added to a given MailChimp list.
The debug log showed no errors.
I eventually uninstalled this plugin.
BUT!!! After about 5 to 10 minutes, the subscriber showed up in the MailChimp list.
Therefore based on my experience of this same or similar problem I conclude that the issue could in fact be with:
a) your web server/host (but the debug log should evidence that)
b) MailChimp (taking some minutes to process and or validate the subscription)
I would suggest the latter B as the likely cause, so as far as MailChimp “swearing this is a wordpress issue” – that’s passing the buck because it can be shown that MailChimp do not always immediately process requests for a variety of reasons.
Current plugin version 1.9 is cetainly broken.
The response result from the API is not being parsed correctly by the plugin logic and additionally the response result from the API appears to be returning an excessive quote prices in excess of $80,000 to ship two small products.
