Once I had a weird electrical event in an apartment building I live in. Suddenly the Residual Current Circuit Breaker with Overload protection (I'm sure it's exactly this kind of device) in the main panel serving my apartment tripped. When I opened the panel it turned out that RCBOs for all the apartments on the same floor also tripped. That looked suspicious and so the next day I inquired with the utility company and they said that dozens of people in several buildings served by the same power substation had the same issue at the same time and the company hotline had an inrush of phone calls.
I don't get it. RCBO should trip when either there's an overload or if there's an imbalance between the phase and the neutral behind the RCBO (between the RCBO and the load). Clearly it's extremely unlikely that dozens of people had either of those at the same time, so I assume that was some external event.
What electrical event could have caused such effect?