Try turning AJAX off on the specific form you are having issues with.
I was having a problem with a WordPress build that was housed in a subdomain where on submission the form would hang on – “One Moment Please…” I had a tool around, and found some useful info on Delicious Days:
https://www.deliciousdays.com/cforms-forum/troubleshooting/cforms-hangs-after-submit-one-moment-please/page-1/
I also found info on the problem being related to subdomains specifically. I’m with hostgator fyi.
Cheers – and great plugin Oliver. Kudos to you and the folks @ DD who do so much to support the WP community. You rock.