Adding centrifugal force in the ground frame — This is the most common error. Only use centrifugal force in the rotating frame (which JEE rarely requires).

Thinking the body flies outward when released — It flies tangentially, not radially outward. At the moment of release, velocity is tangential.

Confusing $v^2$/r and r$omega^2$* — Both give centripetal acceleration, but using v = r*omega. Make sure v and omega are consistent.

Forgetting that centripetal force is not a separate force — It is the NET radial force. Don't add it as an extra force in the free body diagram.

Using T - mg = $mv^2$/r at the top of the loop — This is wrong for a string. At the top: T + mg = $mv^2$/r (both T and mg point toward centre).