I have a condo that I own, and the tenant that just moved in says the master breaker has been tripping every couple of days. I tried to have him identify what was on when the master power switch tripped and the only device/fixture of significant power that may happen to have been on each time is the dyer (definitely on the last two times it tripped, is is unsure if the dryer was on the other times before that) though there is nothing that causes the tripping regularly or like clockwork per say. Also to clarify, the master breaker I am referring to is not in the panel that is located in the condo unit (there is 1 small panel which is 125 amps behind one of the bedroom doors) but the master breaker I am referring to is 1 double pole breaker switch that is located on the exterior of the building and controls the power flow to the entire condo unit.

Almost guaranty that it is a bad connection at the main breaker buss stab. Seen it many times at 100A main breakers.
The bad connection creates a lot of heat and can burn up the stab, fooling the breaker into tripping.

This is not a DIY fix. Please call a pro to come in and replace the breaker. Don't be surprised if he suggests the main disconnect needs to be replaced. Many times this problem takes of the buss stab as well as the breaker.