I want to upgrade from sitefinity 3.6 to 8.0 or higher for a production server.So would like to know the known issue can come for upgradation. we do have custom controls also. any help would be appreciative.
There is no direct path for upgrading from 3.6 to 8. First you need to upgrade to 3.7 and then follow this article: http://docs.sitefinity.com/migrate-sitefinity-3-7-projects