From the linked article:

> [The] stretch of track that was renovated last May and inspected on January 7.

The track had been inspected very recently. Maybe the inspection standards are inadequate?

The linked article also shows figures that are quite meaningless without context.

> [The] vast majority [of Spain's high-speed rail budget] went to new infrastructure with only some 16% earmarked for maintenance, renewal and upgrades. That compares with between 34% to 39% spent by France, Germany and Italy,

They simply can't compare those numbers as-is. Of course Spain will be spending less in maintenance as a percentage of the total budget if it's still mainly building new tracks. It's not a useful figure.

Specifically the fractured track was a soldered joint that joined a track from 1989 with a new one from a few weeks ago.