One of the problems associated with rotor brakes (or wheel brakes for that matter) is the problem of pressure self generation as a result of friction.
Should inadequate clearance exist between the rotor brake pucks and the disc, the resultant friction will generate heat, causing increasing pressure, greater friction, etc, etc. The brake just comes on harder and harder until it catches fire. This situation is extremely dangerous if there is no way of relieving the hydraulic pressure generating in the system, and the cycle is thus self-sustaining.
The situation can be caused by maintenance action, corrosion, slippage prior to rotor engagement, incorrect adjustment and various other causes. I can think of similar rotor brake problems on just about every type of helicopter that has ever flown. The S76 brake problems of long ago related to the brake system itself, but also required that should the brake be immobilised that the lines removed and the brake itself vented to atmosphere, so it could relieve any pressure that might build in the event of a fricion/pressure build up.
This is not to suggest what has occurred here, simply some previous information.
Surprised that the commercial EH-101 did not have a rotor brake installed for North Sea ops. Assume it does for shipboard Naval operations?