When a PID block is the upstream block of a cascade pair, it will go to IMAN as its Actual mode when its downstream partner, (an AO block for example), is not in CASCADE preventing the PID from closing the cascade. Putting the AO block in CASCADE mode usually causes the PID to leave IMAN and return to its Target mode.
Some devices' AO block will not go into CASCADE mode if AUTO is not enabled in the Permitted mode. The Permitted mode can be changed only in Control Studio in edit mode.
Additionally, be sure that the PID's BKCAL_IN is connected to the downstream block's BKCAL_OUT. Failure to make this connection can result in the PID's Actual mode going to IMAN.