Hello John,
I am sorry to see you are running into this issue.
I think it would be helpful to enable debugging and see what takes place when you submit the form on an entry that existed before the upgrade.
To turn debugging on please go to your Control Panel and navigate to Admin->System Administration-> Output and Debugging. Please set the last two settings, which are “Display Output Profiler?” and “Display Template Debugging?”, to yes.
After you enable debugging and submit the form on a pre-upgrade entry, look through the output and note anything suspicious.
Let me know what you see and we will go from there.
Cheers!