What is your company going to do if changing the breaker does not help?
Before we went that route we would install a data logger or considering it is tripping 3 - 4 times daily just use an amp clamp with a memory.
If this breaker is running 320 amps continuously a large motor starting may be enough to trip it out.
Hot weather and it may be a AC unit that is starting up or is simply has an internal problem.
I have not found to many larger breakers that have worn out or gotten weak. No one that I know uses a 400 amp breaker as a light switch.
I would make a rough list of the loads on this breaker and look for equipment that starts 3 - 4 times a day.