Random assortment of thoughts....
Perhaps the Soviets learn the wrong lessons from the Civil War (where all but the core of European Russia was overrun by the Whites). There is a deliberate effort to concentrate industry in Russia proper. That hurts industrialization overall as the easiest areas to site new heavy industry - the Ukraine and the Urals - get less attention. Even worse, it'd put a larger percentage of Soviet Industry in the West where it can be overrun.
One of the obvious ways would be to delay the transfer of war industries to the East. The process was ongoing when Barbarossa began, effectively starting the CCCP off without a great deal of its production capacity. Fortunately the war dragged on the remaining year+ it took to rebuild all the factories and get them running, but if the process had been started later for some reason the Nazis would have "caught" a lot of factories in transit.
Get Stalin a political agreement with a western power about the time militarists start popping up around Europe. It doesn't have to be a thing that would last, or even offer real guarantees. It just has to allay Soviet fears for six months or a year. More factories go on line making consumer goods and such, as per the Five Year Plan. They shift too late, and Russia is much less prepared when the German tanks come rolling in.