The Red Army was caught with their pants down, all right.
The weird thing about this article is that, other than the headline there is no mention of a purge of the sort you describe. It is really about the beginning of an incident at the Siberia-Manchukuo border where Soviet and Japanese army types started shooting at each other.
The incident probably turned into the battle of Khalkin-Gol, fought in a remote area along the Manchurian-Siberian border (heck, what part of the world there isn’t remote?).
The Soviets gave the Japanese a bloody nose, which helped convince the Japanese to go south, not north, in 1941. It also began the rise of a little known Soviet general named Zhukov, who barely missed being purged himself.