I have upgrade from SP 2010 to SP 2013 and also Nintex DB. Problem is that when i check workflow constant at site level they does not exist, when try to create it says Constant already exist.
i also checked database workflow constants are there.
I think this is too specific to be handled in this forum space. I'd suggest you open a ticket at Nintex support. They'll get in touch with you and arrange a web session to check upgrade status, log messages and everything needed to troubleshoot the issues you're having.
