Don’t forget the Brezhnev/Andropov/Chernenko Debacle that led to Gorby...
After B died, the power struggle between the KGB and the State Party Apparatchiks came out full steam.
That, combined with Reagan’s pressure, energy prices, the failure of the 4th 5-Year Plan in 8 Years, massive corruption, and a transport infrastructure that was crumbling led to food shortages, and even riots.
By 1986, reports said less than 15% of the food leaving the farms was arriving in the cities. I was a Soviet Specialist in those days, and there were periods where the west had NO IDEA who was in charge, or even still alive, in the Kremlin.