Not sure about OP, but I do not have CF7 activated in my plugins.
However, your question prompted another idea, this behavior is currently seen during my setup and testing. When I add a manually add subscriber and click ‘resend welcome email’. I have not yet published the newsletter form in my navigation.
I went to the newsletter signup form page instead and entered an email, and the correct Welcome email came through! It appears at least in my case this was only for manually inserted submissions and clicking ‘resend welcome email’.
Now, I’ll have to double check adding subscription using the api, because I’m going to be using that functionality.