Many breakers also have a manual trip, referred to as a '69' switch in ANSI world. If this is pulled out, or there is a defect in the linkage this could cause issues.
Does the breaker have a "Trip Free" feature?
If the breaker is in a tripped condition or if a trip signal is present and an attempt is made to close the breaker without first resetting the trip or removing the trip signal, the Trip Free mechanism will discharge the closing stored energy and immediately discharge the opening stored energy. It appears that the breaker has closed and re-opened. However the link to the contacts has been disabled so that although the mechanism operates and it appears that the breaker has closed and opened, the contacts do not close.
Bill
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"Why not the best?"
Jimmy Carter
Isolate the electrical trip power and close the breaker. If the breaker trips, then you have a mechanical problem. If it does NOT trip, then you start the process of isolating each possible electrical trip path.
I am curious from the amp rating of this "circuit breaker" if it is a recloser, perhaps used as a circuit breaker. If that is the case, it may have a single 14-32 pin connector that when disconnected, removes all connections from the device.
