The buttons are attached to the original URL and will not follow redirects. However, my understanding is that this is possible, that is - so save your shares.
For posts created prior to the SSL upgrade:
function buttons(){
var kCanonical = document.querySelector("link[rel='canonical']").href;
window.kCompositeSlug = kCanonical.replace('https://','http://');
return;
}
buttons();
The above code changes the https:// part of the canonical link for http:// and stores it in a new variable.
What if you are completely changing your domain name? Then try this:
function buttons(){
var kCanonical = document.querySelector("link[rel='canonical']").href;
window.kCompositeSlug = kCanonical.replace('https://newdomain.com','https://olddomain.com');
return;
}
buttons();
Triggering that javascript can be automated to run based on the date the post was published, so all posts published before a scheduled transition are automatically updated, see below:
{% if widget.oldPost %}
Tweet
document.write('</script>');
document.write('');
document.write('');
{% else %}
Tweet
{% endif %}
The above was made to be used within Hubspot, but it should be easy for a developer to chime in & help modify.
For wordpress, try a plugin called Warefare - I cannot attest to the validity of this, and it will cost you as it's a subscription-based service.
This page from addthis academy could also be useful.
I've also been told that support will help you preserve your shares as well, do try reaching out to them.
Best of luck!