I did a database backup from SP 2010 and restored it to SP 2013 Mount-SPContentDatabase followed by site upgrade. Everything looks good except the users did not get converted in claims based. (I can not change my source web application to claim based). users in the groups aren't able to see and perform task and most of these groups have various contribute access. What are my options? SO CRITICAL.
You need to run
Convert-SPWebApplication -Identity http://webAppUrl -From Legacy -To Claims -RetainPermissions:$true.
You will want to do that each time you mount a content database to the claims-enabled web Application.