From my understanding, few very in the early 1980s thought the stability of the USSR was in serious doubt.
Within a decade, though, the entire system collapsed from within and soon ceased to exist altogether. What factors led into this - economic, social, or otherwise?
As a follow up question, were there any political analysts that did predict the end of the USSR early on, and how were they received at the time?
As to factors when contributed to the collapse, here are some:
the policy of openness resulted in a FLOOD of publications about Stalin times: famines, purges, mass deportations, massive mismanagement of prewar years, etc. And then there was another flood:a flood of information about the life on the other side of Iron Curtain: it turned outs that vast majority of people there are not living in dismal poverty and in fact are much better off than an average Soviet citizen. This undermined the trust in Communist party's leadership enormously (which affected the party itself: many people were leaving, many wanted reforms or party split, etc)
USSR had no credible/established country-wide opposition force.. Combined with (1) this was bound to lead to power vacuum (or at least major uncertainty). Which was becoming noticeable around 1988 I guess.
Meanwhile, even a minor economic liberalization, destabilized the centralized economy. Being centralized, the industries of USSR could not adapt quickly enough (and worse, they NEEDED central coordination, any power vacuum in Moscow would be quickly felt throughout the country)
which quickly led to shortages and then rationining of basic consumer goods/food staples. Which led to a vicious spiral of shorages-mean-that-people-spend-more-time-trying-to-find-stuff-to-buy-and-spend-less-time-at-their-work-space-which-leads-to-further-decline-of-production-and-more-shortages...
It's likely that the dropping oil prices were also a major contributing factor to consumer good shortages: https://www.macrotrends.net/1369/crude-oil-price-history-chart (oil was one of the main Soviet exports)
Then some of the ghosts of Stalin's past began to wake up. Baltic states wanted to split. Ethnic tensions flared up in several of the Soviet republics (Uzbekistan, Armenia, Azerbajan). Some of these were badly mismanaged (or even artificially inflamed) by local elites.
Another major contributing factor was almost accidental: Soviet Constitution specifically allowed for the right of secession. I'm sure the right was there mostly to show the world how free USSR was: but it really did not matter: Gorbachev could not pretend to build a law-based society and openly ignore the plain text of constitution. So USSR did get very obvious fault lines..
And then when the coup of 1991 happened and failed, USSR was doomed: pretty much all power in Moscow ended up with the government of Russian Federation (rather than USSR's). And once Russian Federation/Ukraine/Belarus terminated the original union agreement, USSR was no more.