This is such an important point that I would like to affirm as a former US military Soviet intelligence analyst. To be fair, I did not specialize in economics, but I still received a pretty broad education on the Soviet Union in general, and sometimes had access to economic intelligence reports.

In general, (and this is far from being my own private opinion) the US intelligence community missed predicting the imminent fall of the Soviet Union because we tended to believe (not completely believe, but nonetheless generally believe) Soviet managers who reported up the chain that things were going just fine.

The Soviet system predisposed them to not admitting their own failures, which tended to be systemic rather than personal anyway. Even mid-level managers could not admit their failures. Rosy pictures got sent all the way up to Politburo level, and while leaders at the highest levels understood to some extent that the data was misleading, they could not admit their own failures either. The extent of the economic dysfunction was not appreciated until the economy collapsed in on itself — not appreciated by Soviet leaders intensely invested in denying it, and not appreciated by the broader global intelligence community who should have known what they were looking at.