> The ground connections of Hydro-Québec’s transmission system of high-tension lines and transformers eventually started conducting some of these earth currents, and at 2:43 AM, protective circuit breakers tripped at the Chibougamau substation in central Québec. This caused an imbalance on a 750 kV transmission line, which tripped breakers 150 km away.

> Within one minute, the cascading failures ...

So the actual problem was that all their power grid was turned off... ie. disconnected... ie. high impedance... ie. the most vulnerable state.

Operational changes could be made so that all 'tripped breakers' lead to at least one or other side of the breaker being grounded rather than left open circuit, which would solve the problem. That only needs to be the case during a solar storm, and electrical power lines are frequently grounded during maintenance for safety anyway.