You can't get an "informed opinion" by reading crap like that report.

The Spanish systems have systematic design failures for stability and electricity market design. Working out the political failures that led to the design failures is much harder.

Consultancies like https://www.nera.com/capabilities/power--utilities--and-rene... specialize in advising about electricity networks and market design.

Only those working closely in that profession have any knowledge of the underlying causes.

Most everyone else (including this comment) is different levels of ignorance and cluelessness.

Edit E.g. Crap quote from the report "but no significant oscillations with amplitudes above 20 mHz". The rest of it is about that level from what I could tell.