Ok I figured it out, it seems that ssl_stapling was causing issues for certbot. Once I commented out the following lines in my nginx.conf, I was able to renew my cert:
ssl_stapling on;
ssl_stapling_verify on;
Not sure if it's a bug from certbot's end, but it seems it has issues with ssl_stapling? In any case, hopefully this helps someone with the same/similar issues.