There were several major events that the KGB either failed to predict or misjudged, e.g., it
underestimated the Solidarity movement in Poland
failed to predict the fall of the Berlin Wall
did not foresee the fall of the USSR itself
I can also add massive disasters with Chernobyl and the outcome of the Afghan War, which were also due to the KGB failing to provide accurate info and predict dangers.
Was the KGB, at least after 1975, actually an efficient institution in any way? Or was it just a propaganda tool and a provider of sinecures for its staff?