Issue :
After migration of servers, the reseller (logged in with the root password) is unable to access the users’ control panel.
Fix :
Go to WHM >> Main >> Tweak Settings and check if the following option is enabled :
“Disable login with root or reseller password into the users’ cPanel interface. Also disable switch account dropdown in themes with switch account feature.”
If yes, then un-check it and the issue should be resolved!