Fails to add user to list - have to recreate mapping after list updates

I have one gravity form that adds new customers to 2 MailChimp lists.

Subscribers are added to both lists correctly - until I make an update to one of the list's group configuration.

Here's the specific scenario:

User submits form
User is added to List A, Group A
User is also added to List B
Success!

(I go in and add Group B to List B and re-run the scenario)

User submits form
User FAILS to be added to List A
User is added to List B, Group B

(I go in and delete the MailChimp Mapping for List A and re-add it)

Now the scenario succeeds on both lists.

This happens every time that I make changes to the groups in one of the lists.
I have to delete the mapping to the other list and recreate it.

Is this a bug?

Hmmm... After testing this THOROUGHLY :-). This may actually be an error from re-using test data. I found some weirdness with emails sometimes getting added but not always, so I created a completely new set of test data and have not been able to reproduce this error since then.

Now I'm thinking that MailChimp was silently failing when the email had been submitted but not confirmed (the list that's giving me issues is a double optin list) - those emails don't show up when you query subscribers so it would look like they are not there but they are...

Is there any way to see the Gravity Forms logs to confirm this?
Or does anyone know how to see unconfirmed subscribers on MailChimp?

Interesting day... :-)

I did confirm that re-using test data was my issue. I made sure to delete the users from WordPress and the active users from MailChimp - but I can't see unconfirmed users in MailChimp and they are not getting deleted.

So when I run the test again with a previously used email - I don't see the welcome message and don't see the use added in MailChimp because he's in a limbo (not confirmed) state... so it looks like he's not getting added to the list.

At least I have the answer...