Someone elsewhere posted this quote from the Guardian:

He says that around 8:30am this morning, the LZB controlling system failed due to communications issues, leaving no coverage for just over 60km of the track, which in turn triggered an automatic stop for six trains on that stretch.

But around 8:36, the Adif control centre issued a manual instruction to override the warning and let the traffic resume.

He heavily suggests that this “inexplicable” decision should not have been made, as trains should have remained under strict orders not to move.

The fail state is a restricted speed. That restriction is typically 40 km/h or 50 km/h, depending on the country. From that speed you can still stop the train in time if you see an obstacle, and that is completely safe.

But that is mandated by a rule, not by technology. And for some reason the train dispatcher gave an order to continue with normal speed, that is: full speed.